Contents

CHAPTER IX

Heat Casualty

Ludwig M. Eichna, M.D.

The global nature of World War II required men to live, work,and fight in climatic extremes far in excess of any to which most of them hadever before been exposed.¹ This was particularly true of the hotclimates, and troops were stationed in many of the hottest regions on earth. Layopinion had long maintained the traditional belief that the white men could notendure very hot climates. The natives of these areas were believed to havegained, over the centuries, special adaptations to life in such environmentalextremes. It was said of certain hot regions that their climate, and endemicdiseases, proved a more dangerous adversary than the enemy. How did the soldierfare and perform in such hot climates? The answer is: "Well-after he had learned several fundamentalrules."

The experience of the military forces in hot climates, andthe lessons learned, can be briefly summarized. When troops first entered a hotregion, regardless of whether it was in the United States or overseas-in thearid desert or the humid jungle-a considerable number of heat casualties wereencountered. Accumulation of knowledge and experience led to effectivepreventive measures, so that the problem of heat casualty was greatly reduced.In the last years of the war, it was concluded that, although environmental heatconstituted an added handicap to troops, hot climates were well tolerated anddid not prevent effective military operations. Military experience demonstrated,from the physiological standpoint, that hot climates are not the exclusivedomain of their natives and that the white man, once he has learned, can livehealthfully and work efficiently in extreme heat.

ENVIRONMENTAL TEMPERATURE

Although a discussion of the environmental features of thehot climates cannot be undertaken here, some data indicating the heat loadsimposed upon troops by the climates of representative hot areas will bepresented. Adequate climatic data are scarce, and the only systematicmeteorological data were collected by the Army Air Forces. Other reports, inwhich air

¹The discussion in this chapter deals solely with those effectsof heat as a physical agent imposing a thermal load which man must dissipate.His inability to maintain the required compensatory adjustments leads tosystemic changes which render him a casualty, hereafter termed "heatcasualty," "casualty from heat," "ill effects of heat,""heat disability," or "adverse effects of heat."

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temperature is mentioned secondarily, present data obtainedunder many varying conditions and usually only the highest readings arerecorded. As a rule, the dry bulb temperatures²were obtained, and the more important wet bulb temperatures or dewpoint readingsare lacking. With these limitations, table 39 indicates the climatic conditionsfor representative hot areas occupied by U.S. troops.

TABLE 39.-Climatic conditions inrepresentative hot areas where U.S. troops were stationed

Area	Air (dry bulb) temperatures	Approximate relative humidity1
	?F.	Percent
Desert:
Southwestern United States	110-122	10-15
Iran	112-126	10-15
Semidesert:
India (dry monsoon)	98-118	20-30
Tropical:
Burma	98-110	50-65
Southwest Pacific Islands	93-112	50-65
Semitropical:
Southeastern United States	93-108	35-50

¹Estimated representative humidityduring hot season in each area. At peak dry bulb temperatures, humidities areoften lower.

These temperatures give only a partial picture. They arebased on observations made near fixed installations usually constructed inclearings and often near the seacoast with its moderating winds. Few data areavailable from areas deep within the jungle or the desert or from foxholes,caves, dugouts, tents, and other combat positions. Additional heat loads werealso imposed upon men in closed spaces; for example in "buttoned"tanks, in truck cabs, in grounded planes, in ships and ships' holds, instorehouses, and in kitchens. The environment in such spaces may be much morerigorous than that of the outside air (table 40).³

Finally, the heat stress of an environment cannot be definedcorrectly by individual temperature readings without considering the duration ofelevated temperatures and of humidities. Moderately high temperatures, continuedthroughout the day and night, subject personnel to greater physiologicalstresses than do much higher temperatures in the daytime, followed by relativelymilder nights. The desert areas and small islands thus impose

²A thermometer in air, shielded from the sun, measures the air, "dry bulb," temperature; when the bulb of the thermometer is covered with a wetted wick and the thermometer is swung in air, a lower, "wet bulb," temperature is obtained, because of the evaporative cooling from the wick. The degree of lowering of the temperature is a function of the moisture content of the air.
³Adolph, E. F.: Tolerance to Heat. Report No. 1, Contract No. OEM-cmr 483, for Committee on Medical Research, Office of Scientific Research and Development, 1 Feb. 1945.

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TABLE 40.-Maximal climatic conditions ofinstallation in representative areas, by locationandclosed spaces

Location	Temperature		Relative humidity	Installation	Temperature		Relative humidity
	Dry  bulb	Wet bulb			Dry bulb	Wet bulb
	?F.	?F.	Percent		?F.	?F.	Percent
Iran	120	---	---	Tent	137	---	---
Louisiana	97	76.5	---	Buttoned tank after 4-hour run	123	91	---
Philippine Islands:
Luzon	91	79	59	Turret of stationary buttoned tank	98	93	84
Do	88	80	70	Loaded transport plane before takeoff	97	88	70
Offshore	90	80	65	Tank deck (landing ship, tank)	109	90	48

Source: (1) Data for Iran and its installation: History ofMedical Section, U.S. ArmyForces in the Middle East, September 1941 to September 1945. [Official record.]
(2) Data for other locations and installations: Personalobservations of the author, 1944 and 1945.

a somewhat lesser heat stress and inland tropical areas agreater stress than their peak temperatures would indicate.

INCIDENCE

The incidence of heat casualty in World War II is notaccurately determinable, for the following reasons: (1) The confusion regardingdiagnosis, largely because medical officers were not familiar with the illeffects of heat; (2) the coexistence of other conditions, particularly woundsand injuries on which attention was focused primarily; and (3) the difficultiesof recordkeeping on a global scale. With these shortcomings in mind, tables 41,42, 43, and 44 present statistics on heat casualty in the U.S. Army in World WarII.⁴ The data include admissionsfor heatstroke, heat exhaustion, and certain other ill effects of heat during1942-44.

Tables 41, 42, and 43 indicate that, in terms of admissionrates per 1,000 average strength per year, heat casualty never became a majormedical problem for the Army at any time during the war. Thus, for the totalArmy, the admissions per 1,000 average strength per year were as follows: For1942, 2.03; for 1943, 2.54; and for 1944, 0.88. These data are to be comparedwith the peacetime (1940) rates of 0.5 for the Army in the United States, 1.4for the Army in Panama, and 1.3 for the Army in the Philippines. The wartimeincrease in the admission rates for heat

⁴Unless otherwise indicated, the statistical analysis of theill effects of heat in the U.S. Army in World War II is based on data compiledby the Medical Statistics Division, Office of The Surgeon General, Departmentof the Army.

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TABLE 41.-Admissions for ill effectsof heat (excluding sunburn and burns), in the U.S. Army, by area and month, 1942

[Rate expressed as number of admissions perannum per 1,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Area	Total number  of  admis- sions	Rate
		Total	Jan- uary	Feb- ruary	March	April	May	June	July	August	Septe- mber	Octo- ber	Nove- mber	Dece- mber
Continental United States	5,852	2.20	0.03	0.01	0.10	0.27	1.30	4.13	12.49	5.80	2.29	0.25	0.06	0.03
Overseas:
Europe	4	0.05	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.40	0.00	0.00	0.00	0.00
Mediterranean1	2	.09	(2)	(2)	(2)	(2)	(2)	(2)	(2)	(2)	(2)	(2)	.00	.13
Middle East	35	5.78	(2)	(2)	(2)	(2)	(2)	22.22	9.52	15.02	15.45	4.66	4.58	.94
China-Burma-India	92	10.52	(2)	(2)	7.55	.00	10.97	70.80	42.86	8.71	1.77	2.66	.00	.00
Southwest Pacific	122	1.72	6.38	3.64	2.95	.24	.17	.44	.13	.83	.97	1.62	2.52	5.85
Central and South Pacific	174	1.15	.43	.85	3.41	1.60	.88	1.49	.75	.66	.62	.40	1.09	2.23
North America3	8	.08	.00	.00	.00	.00	.00	.00	.72	.09	.00	.00	.00	.00
Latin America	114	1.12	.99	1.60	2.03	1.54	.86	.58	.75	.43	1.60	1.16	.96	1.18
Total overseas4	727	1.24	0.94	1.55	2.34	0.95	3.92	1.64	1.15	0.70	0.85	0.59	0.72	1.33
Total Army	6,579	2.03	0.13	0.20	0.40	0.38	1.74	3.69	10.32	4.78	2.00	0.31	0.20	0.28

¹Includes North Africa.
²Few or no troops in area.
³Includes Alaska and Iceland.
⁴Includes admissions (176) on transports.
NOTE.-The 0.00 indicates a rate ofless than 0.005.

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TABLE 42.-Admissions for ill effects ofheat (excluding sunburn and burns), in the U.S. Army, by area and month, 1943¹

[Rate expressed as number of admissions perannum per 1,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Area	Total number  of  admis- sions	Rate
		Total	Jan- uary	Feb- ruary	March	April	May	June	July	August	Septe- mber	Octo- ber	Nove- mber	Dece- mber
Continental United States	14,470	2.79	0.05	0.10	0.07	0.41	1.75	7.28	11.15	8.92	1.83	0.16	0.01	0.06
Overseas:
Europe	8	0.03	0.00	0.00	0.00	0.00	0.00	0.00	0.11	0.14	0.08	0.00	0.02	0.00
Mediterranean2	713	1.56	0.05	.00	.00	.41	1.67	3.63	5.84	3.42	1.95	.06	.00	.02
Middle East	1,103	20.80	.73	.00	1.43	1.15	15.41	17.30	57.45	88.59	21.91	2.40	.00	.00
China-Burma-India	92	2.32	.00	.66	1.08	.44	8.91	6.56	6.18	1.57	4.80	.62	.50	.00
Southwest Pacific	386	2.03	3.36	3.59	2.69	1.57	1.02	.50	.93	1.28	1.20	2.75	2.58	3.04
Central and South Pacific	460	1.58	2.80	3.25	1.46	1.31	1.23	.26	1.00	.68	3.07	1.37	1.48	1.55
North America3	4	.02	.00	.00	.00	.00	.00	.00	.15	.00	.00	.00	.00	.00
Latin America	97	.80	1.48	82	1.13	.69	.37	.60	1.06	.96	.50	1.02	.52	.34
Total overseas4	2,934	1.74	1.13	1.29	0.77	0.65	1.76	2.06	4.45	4.61	2.07	0.72	0.61	0.61
Total Army	17,404	2.54	0.26	0.33	0.20	0.46	1.76	6.12	9.52	7.82	1.89	0.32	0.19	0.24

¹Excludes 4 admissions characterizedas battle injuries, for which the monthly distribution is not available.
²Includes North Africa.
³Includes Alaska and Iceland.
⁴Includes admissions (71) on transports.
NOTE.-The 0.00 indicates a rate ofless than 0.005.

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TABLE 43.-Admissions for ill effects ofheat (excluding sunburn and burns), in the U.S. Army, by area and month, 1944¹

[Rate expressed as number of admissions perannum per 1,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Area	Total number  of  admis- sions	Rate
		Total	Jan- uary	Feb- ruary	March	April	May	June	July	August	Septe- mber	Octo- ber	Nove- mber	Dece- mber
Continental United States	4,299	1.08	0.01	0.05	0.06	0.14	1.04	3.58	3.82	2.84	1.27	0.05	0.01	0.00
Overseas:
Europe	75	0.04	0.00	0.00	0.05	0.05	0.12	0.00	0.11	0.19	0.03	0.00	0.00	0.00
Mediterranean2	196	.30	.02	.06	.06	.07	.23	.64	1.19	.97	.04	.11	.00	.00
Middle East	158	3.41	1.20	.26	.00	1.37	3.02	15.76	14.37	4.87	.27	.49	.00	.00
China-Burma-India	525	3.11	.00	.00	.40	2.77	13.31	13.21	3.57	2.79	.67	.28	.17	.15
Southwest Pacific	1,061	1.97	3.21	2.59	2.49	1.97	2.40	2.17	1.03	1.08	1.28	3.54	1.99	1.01
Central and South Pacific	391	.89	1.48	.73	.89	.59	.74	1.64	1.05	.70	.71	.68	.75	.80
North America3	4	.03	.00	.00	.00	.00	.00	.28	.10	.00	.00	.00	.00	.00
Latin America	31	.36	.72	.53	.37	.13	.13	.72	.14	.15	.62	.60	.00	.15
Total overseas4	2,535	0.67	0.66	0.53	0.52	0.52	1.19	1.45	0.89	0.71	0.35	0.66	0.40	0.25
Total Army	6,834	0.88	0.24	0.24	0.25	0.31	1.11	2.55	2.36	1.75	0.78	0.39	0.23	0.15

¹Excludes 107 admissions characterizedas battle injuries, for which the monthly distribution is not available.
²Includes North Africa.
³Includes Alaska and Iceland.
⁴Includes admissions (94) on transports.
NOTE.-The 0.00 indicates a rate ofless than 0.005.

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TABLE 44.-Summary of heat casualties in the UnitedStates, by area, installation, and unit, 1942-43

Area and installation	Unit	Date	Heat casualties			Remarks
			Total number	Number hospi- talized	Number of deaths
Southeastern United States.1	Fourth Service Command.	1 Jan.-26 Aug. 1942.	1,307	378	13	Data compiled from 21 stations (see table 48).
Fort Eustis, Va.2	Station Hospital.	1942	---	49	---	Fifth in frequency of hospital admissions.
Fort Eustis, Va.3	...do...	Summer of 1943.	273	---	2	Major medical problem in the summer.
Camp McCain, Miss.4	87th Infantry Division.	July and August 1943.	---	164	3
Camp Van Dorn, Miss.5	99th Infantry Division.	6 Apr.-11 Sept. 1943.	300	---	2
Desert Training Center, southern California.6	77th Infantry Division.	1943	649	183	---
Desert Training Center, southern California.7	...do...	8 Apr.-23 Sept. 1943.	409	25	---
Desert Training Center, southern California.7	...do...	8 and 9 June 1943.	73	---	---	Fell out during marching in heat.
Desert Training Center, southern California7	...do...	26-29 June 1943.	68	---	---	Strict water discipline.
Desert Training Center, Indio, California.8	7th Armored Division.	26 June-15 July 1943.	51	44	---	On maneuvers for 20 days.

¹Letter, Headquarters, Fourth Service Command, to The SurgeonGeneral, 26 Aug. 1942, subject: Report of Cases of Heat Stroke and HeatExhaustion.
²Annual Report, Station Hospital, Fort Eustis, Va., for 1942.
³Annual Report, Station Hospital, Fort Eustis, Va., for 1943.
⁴Annual Report, 87th Infantry Division, for 1943.
⁵Annual Report, 99th Infantry Division, for 1943.
⁶Letter, Office of the Division Surgeon, Headquarters, 77th InfantryDivision, to Commanding General, 77th InfantryDivision, 3 Aug. 1943, subject: Summary of Medical Experiences and Problems onDesert Maneuvers.
⁷Sneidman, G. I.: Exhaustion and High Temperatures as Experienced in DesertOperations. [Professional paper.]
⁸Annual Report, 7th Armored Division, for 1943.

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TABLE 45.-Deaths due toenvironmental heat, in the U.S. Army, by area and cause of death, 1942-45

[Rate expressed as number of deaths per annum per 100,000average strength]
[Preliminary data based on complete files of individualmedical records]

Area and cause of death	1942-45		1942		1943		1944		1945
	Number of deaths	Rate	Number of deaths	Rate	Number of deaths	Rate	Number of deaths	Rate	Number of deaths	Rate
Continental United States:
Heatstroke	153	1.04	46	1.73	82	1.58	15	0.38	10	0.34
Heat exhaustion	25	.17	6	.23	12	.23	7	.18	---	0
Other	24	.16	6	.22	17	.33	1	.02	---	0
Total	202	1.37	58	2.18	111	2.14	23	0.58	10	0.34
Overseas:
Heatstroke	17	0.16	1	0.17	7	0.41	16	0.16	3	0.06
Heat exhaustion	11	.10	---	0	3	.18	5	.13	3	.07
Sunburn	1	.01	---	0	---	0	1	.03	---	0
Other	8	.08	2	.34	4	.24	2	.05	---	0
Total	37	0.35	3	0.51	14	0.83	114	0.37	6	0.13
Combined continental United States and overseas:
Heatstroke	170	0.67	47	1.45	89	1.29	21	0.27	13	0.17
Heat exhaustion	36	.14	6	.18	15	.22	12	.15	3	.04
Sunburn	1	2.00	---	0	---	0	1	.01	---	0
Other	32	.13	8	.25	21	.31	3	.04	---	0
Grand total	239	0.94	61	1.88	125	1.82	37	0.47	16	0.21

¹Includes one death among transportadmissions.
²Indicates a rate of more than zerobut less than 0.005.

casualty, which occurred chiefly in the first 2 years of thewar, was obviously not great. Nevertheless, because of the large number of menmobilized, the relatively low admission rates represent sizable numbers ofpatients, as follows: In 1942, 6,579 heat casualties with 61 deaths; in 1943,17,404 heat casualties with 125 deaths; in 1944, 6,834 casualties with 37deaths; and in 1945, 4,470 heat casualties with 16 deaths (tables 41, 42, 43,and 45). The study made by the Army Institute of Pathology, Washington, D.C., ofthe necropsy material from 125 of the 190 fatal cases of heatstroke whichoccurred in troops in the United States during the summer months of the 4-yearperiod 1941 to 1944, inclusive,⁵ is believed to be the largest series of fatalheatstroke analyzed.

⁵Malamud, N., Haymaker, W., and Custer, R. P.: HeatStroke, AClinico-Pathologic Study of 125 Fatal Cases. Mil. Surgeon 99: 397-449, November1946.

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Hospital admission rates are inadequate indexes of the extentof the problem, for they indicate only the outright heat casualties. In allhot regions, there were many men who were not sufficiently incapacitated toreport to sick call and who were confined to quarters or "stuck itout," working inefficiently or not at all. These men were, in truth, heatcasualties to the effectiveness of the Army; but most of them were never placedon sick lists and their numbers are unknown.

Moreover, since heat casualty has a seasonal incidence, ananalysis which averages the low incidence of the cool months with the highincidence of the hot months does not fully present the problem. Thus, the yearlyadmission rate for an area may be low, but in the hot months heat casualty maybe a serious problem to a particular command. In the same manner, data averagedfor large areas do not represent the problem in the component commands withinthe large area. The urgency and magnitude of heat casualty in individual units,for example, the Desert Training Center in southern California, may be seriousand yet be completely masked when averaged with the low incidence in the coolercomponents of the theater, such as the northern United States. Therefore, theaverage yearly rates will require revision if the true significance of the illeffects of heat is to be appreciated in the units affected. An analysis of heatcasualty by area and month is recorded in tables 41, 42, and 43.

Heat casualties assumed significant proportions in the Armyin only three areas: The China-Burma-India theater, the Middle East theater, andthe United States. High rates were temporary and largely limited to the periodimmediately after arrival in the areas. In the China-Burma-India theater,casualties for 1942 reached 10.52 per 1,000 per year, with a peak incidence of70.80 per 1,000 per year for the month of June (table 41). Although heatcasualty threatened to become a serious problem, the comparatively small numberof troops in the theater at this time resulted in 92 admissions with 2 deaths.In the next 2 years, the incidence by month, and for the year, was decidedlylower, and heat casualty no longer constituted a significant medical problem inthis theater.

In the Middle East theater, owing almost entirely to the highincidence in the Persian Gulf Command⁶ (table 46), heat casualty in 1943reached 20.80 per 1,000 per year with 1,103 admissions for the year (table 42).In the summer months of July and August 1943, when the rates reached 57.45 and88.59 per 1,000 per year, respectively, heat casualty became a major medicalproblem. A striking decrease occurred in the following year (table 43), when theyearly incidence fell to 3.41 per 1,000, the peak (June) incidence to 15.76 per1,000, and total admissions to 158.

In the United States, heat casualty presented a somewhat different problem. The admission rates per 1,000 per year were always relatively low (2.20, 2.79, and 1.08 for 1942, 1943, and 1944, respectively), but be-

⁶Annual Report, U.S. Army Forces in the Middle East, for 1943.

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TABLE 46.-Incidence of heatcasualty in U.S. Army Forces in Middle East, by area or command, from 1 July1942 to 1 October 1943

[Incidence expressed as number of heat casualties admitted tohospital or quarters or both]

Area or command	Heat exhaustion	Heatstroke	Sunburn	Miscellaneous	Total
Eritrea	50	---	1	49	100
Libya	8	---	2	---	10
Delta	6	1	6	5	18
Levant	2	---	1	---	3
Headquarters, USAFIME	---	---	---	---	---
Air Force	20	---	4	---	24
Persian Gulf	1,070	16	10	92	1,188
West Africa	---	---	1	---	1
Total	1,156	17	25	146	1,344

Source: Annual Report, U.S. Army Forces in the Middle East,for 1943.

cause of the large number of men intraining, the total number of patients exceeded that of all other theaterscombined (tables 41, 42, 43, 47, and 48). In 1942, there were 5,852 cases with58 deaths; in 1943, 14,470 cases with 111 deaths; and in 1944, 4,299 cases with23 deaths.⁷ These data are for the whole of the United States,whereas the heat casualties occurred in camps in the Southern States. It is ofinterest that the largest number of casualties and deaths due to heat occurredin troops in the United States where the climate, even in the southeast andsouthwest, is not ordinarily considered hot when compared with the climate ofIndia, Burma, or Iran.

Since overall statistics tend to minimize the problemsencountered by individual units placed in climatic extremes, it seemsappropriate to list some of the more serious experiences with heat casualtysustained by different units in the United States (see table 44).

The illustrations given in table 44 were chosen from unitsreporting high casualty rates. Other units in the same areas did not mentionheat casualty. This may have been an omission or such units may have profited bythe example of their predecessors and neighbors and instituted measures whichreduced heat casualty to such a minor role that it was not deemed worthy ofnote. Nevertheless, heat casualties were still frequent in troops in theUnited States (tables 43 and 45), and a survey from 1 to 31 August 1944 revealed18 stations reporting 6 or more cases during this period (table 49).

Illustrative examples from oversea theaters are moredifficult to obtain. In the Middle East, casualty from heat accounted for11.7 percent of hospital admissions in the Persian Gulf Command, from 6 June to9 December 1942, and was exceeded in importance only by enteritis (28 percent)and

⁷In 1945, there were 2,315 admissions with 10 deaths.

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TABLE 47.-Admissions and deathsfor heat casualties among troops in the United States, by month and year, January-December, 1942, 1943, and 1944

[Rate for admissions expressed as number of admissions perannum per 1,000 average strength]
[Rate for deaths expressed as number of deaths per annum per100,000 average strength]
[Preliminary data based on sample tabulations of individualmedical records]

Month	1942		1943		1944
	Number	Rate	Number	Rate	Number	Rate
	Admissions1
January	4	0.03	20	0.05	4	0.01
February	2	.01	40	.10	18	.05
March	16	.10	30	.07	23	.06
April	47	.27	180	.41	53	.14
May	248	1.30	805	1.75	370	1.04
June	822	4.13	3,250	7.28	1,200	3.58
July	2,693	12.49	5,165	11.15	1,296	3.82
August	1,352	5.80	4,080	8.92	932	2.84
September	569	2.29	800	1.83	386	1.27
October	70	.25	70	.16	13	.05
November	18	.06	5	.01	4	.01
December	11	.03	25	.06	---	0
Total	5,852	2.20	14,470	2.79	4,299	1.08
	Deaths2
January	---	0.00	---	0.0	---	0.0
February	---	0	---	0	---	0
March	---	0	---	0	---	0
April	---	0	---	0	---	0
May	1	.52	4	.87	1	.28
June	3	1.51	18	4.03	5	1.49
July	32	14.85	63	13.60	4	1.18
August	15	6.43	26	5.68	8	2.44
September	7	2.82	---	0	5	1.64
October	---	0	---	0	---	0
November	---	0	---	0	---	0
December	---	0	---	0	---	0
Total	58	2.18	111	2.14	23	0.58

¹There were 2,315 admissions in 1945.
²There were 10 deaths in 1945.

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TABLE 48.-Heat casualties in Fourth ServiceCommand, by station, 1 January-26 August 1942

Station	Heat casualties
	Total number	Number hospitalized	Number of deaths
Fort Barrancas, Fla.	6	6	---
Fort Benning, Ga.	15	15	1
Camp Blanding, Fla.	8	8	---
Fort Bragg, N.C.	107	107	5
Camp Croft, S.C.	86	86	1
Camp Davis, N.C.	12	12	---
Camp Forrest, Tenn.	---	---	---
Camp Gordon, Ga.	9	4	---
Fort Jackson, S.C.	31	31	---
Key West Barracks, Fla.	1	1	---
Fort McClellan, Ala.	511	(1)	2
Fort McPherson, Ga.	---	---	---
Fort Moultrie, S.C.	1	1	---
Fort Oglethorpe, Ga.	6	6	---
Camp Rucker, Ala.	28	28	---
Fort Screven, Ga.	---	---	---
Camp Shelby, Miss.	5	---	---
Camp Stewart, Ga.	11	11	---
Camp Sutton, N.C.	26	26	---
Camp Tyson, Tenn.	1	1	---
Camp Wheeler, Ga.	443	35	4
Total	1,307	378	13

¹Statistics were not furnished.

venereal disease (12 percent).⁸In the same theater from 1 July 1942 to 1 October 1943,1,344 heat casualties represented 2.5 percent of all admissions.

The 113th General Hospital arrived at Ahvāz, Iran, on 28 May1943 and by the end of the year had treated 8 cases of heatstroke, 221 casesof heat exhaustion, and 124 cases of ill-defined effects of heat; a total of353.⁹ Apart from the Persian Gulf Command, heat casualties in other partsof the Middle East in 1942 and 1943 were few, except for Eritrea, where 99 casesoccurred during the period from 1 July 1942 to 1 October 1943 (table 46).

Most reports from the Central and South Pacific and theSouthwest Pacific do not mention heat casualty, or pass over it in generalterms. There are some exceptions. The annual report for 1942 of the Office ofthe Surgeon,

⁸History of Medical Section, U.S. Army Forcesin the Middle East, September1941 to September 1945. [Official record.]
⁹Annual Report, 113th General Hospital, for 1943.

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TABLE 49.-Stations in the UnitedStates reporting six or more casualties from ill effects of heat between 1 and 31 August 1944

[Rate expressed as number of admissions perannum per 1,000 average strength]

Service Command	Station	Strength	Heat casualties
			Number	Rate
First	Fort Devens, Mass.	13,500	8	7
Third	Aberdeen Proving Ground, Md.	24,782	9	4
Do...	Fort Lee, Va.	34,653	6	2
Fourth	Fort Benning, Ga.	71,447	25	4
Do...	Camp Blanding, Fla.	56,049	60	13
Do...	Camp Croft, S.C.	20,195	8	5
Do...	Camp Rucker, Ala.	30,057	15	6
Do...	Camp Van Dorn, Miss.	33,170	8	3
Fifth	Camp Breckinridge, Ky.	35,249	9	3
Do...	Fort Knox, Ky.	34,625	6	2
Seventh	Fort Riley, Kans.	29,897	13	5
Eighth	Camp Barkeley, Tex.	44,516	25	7
Do...	Camp Chaffee, Ark.	27,665	17	7
Do...	Camp Claiborne, La.	49,208	11	3
Do...	Fort Hood, Tex.	60,869	77	15
Do...	Camp Joseph T. Robinson, Ark.	38,501	35	11
Do...	Camp Maxey, Tex.	31,796	15	6
Ninth	Camp Roberts, Calif.	33,176	26	9

U.S. Army Forces in the South Pacific Area, in referring tothe activities on Guadalcanal states: "The major medical problems werebattle casualties, malaria, dysentery, tropical ulcers, and heatexhaustion."¹⁰ In a reportdated 20 February 1943, the surgeon of the 101st Medical Regiment, attached tothe Americal Division, considered heat exhaustion a medical problem which inorder of frequency of medical admissions stood 10th, with 141 admissions up to14 February 1943, as compared to 3,102 admissions for malaria (first in thecause of medical admission) over the same period.¹¹ The leadingmedical causes for admission to three field hospitals of the 101st MedicalRegiment were as follows:

Cause	Number of cases
Malaria (all types)	3,102
Nervous disorders	483
Enteritis	416
Cellulitis	411
Fever of unknown origin	343
Upper respiratory infection	302
Jaundice	248
Skin disease	234
Otitis media	227
Heat exhaustion	141

¹⁰Annual Report, U.S. Army Forcesin the South Pacific Area, for 1942.
¹¹Annual Report, 101stMedical Regiment for 1942, with enclosure 8 thereto, dated 20 Feb. 1943.

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In the 25th Infantry Division during operations onGuadalcanal, New Guinea, and Morotai (1943 and 1944), heat exhaustion causedfrom 5 to 10 percent of all medical casualties and occurred chiefly in troops onthe offensive or on forced marches.¹² For the 41st Infantry Division, thefollowing was noted:

Especially in the Hollandia operation and the present Biaklanding, heat exhaustion cases have been third in the cause of hospitaladmission. Experience has also shown diminution of combat efficiency in many more personnel who were not prostrated to the extent ofrequiring hospitalization.¹³

In the China-Burma-India theater, the hot humid climate ledto lethargy and decreased efficiency of work, but frank heat casualty wasinfrequently encountered after 1942. Even so, in Gaya, India, during June 1945,when the air temperature reached 113? F., eight cases of heat exhaustion weretreated at the 99th Station Hospital, with one death.¹⁴ The islandsin the Pacific Ocean Area do not, for the most part, have hot climates, and thereports do not list heat as a cause of casualty there. Similarly, reports fromthe Mediterranean, South Atlantic, and Caribbean Commands either fail to mentionheat casualty or routinely state "no ill effects of heat," leading tothe conclusion that in these areas climate can be disregarded as a detrimentalfactor.

In summary, heat casualty constituted a medical problemwhich, though by no means a major one, could not be ignored. In absolutenumbers, many men became casualties because of heat, and in specific areas, atgiven times, the problem was serious and urgent.

Decrease in Incidence

The incidence of heat casualty in all hot theaters decreasedsteadily as the war progressed, until in the last year of the war it became aminor medical problem, even in the hottest areas. The experience in the MiddleEast theater is a striking example of this reduction. Troops moved into thistheater in the last half of 1942 and the first half of 1943. The summer of 1943found a considerable body of troops exposed to the hot desert for the first timein their lives. Heat casualties for 1943 numbered 1,103 cases with an admissionrate of 20.80 per 1,000 per year and, in August, a peak monthly incidence of88.59 per 1,000 per year (table 42). In 1944, however, the number of casesdeclined to 158, the yearly admission rate to 3.41 per 1,000 per year, and thepeak monthly (June) incidence to 15.76 per 1,000 per year (table 43). Theexperience in the Persian GulfCommand set the pattern for the entire theater. This marked reduction in heatcasualty was achieved, with the command breaking all records moving supplies,

¹²U.S. Army Forces, Far East, Board Report No. 145,Questionnaire of Armored Medical Research Laboratory on Problems of JungleWarfare.
¹³Annual Report, 41st InfantryDivision, for 1944 (2d quarter).
¹⁴Personal correspondence, medical officer in India, toauthor.

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even though the summer of 1944 was as hot as the summer of1943. Individual unit figures showed the same improvement.

The experience of the Persian Gulf Command is especiallysignificant since this was the hottest theater in which troops were stationedfor long periods. The final opinion of the Command was that, once it had learnedand instituted proper living conditions, proper working hours, and properhandling of troops, it could maintain effective work without significant illnessfrom the heat.

In the China-Burma-India theater, the experience wasessentially the same. During the first year (1942), the admission rate was 10.52per 1,000 per year and the peak monthly rate, 70.80 per 1,000 per year. In1943, these rates fell to 2.32 and 8.91, respectively, and in 1944 they were3.11 and 13.31 (tables 41, 42, and 43). The fact that the total yearly caseloadincreased from 92 in 1942 to 525 in 1944 was a reflection of the increasednumber of troops in the theater, for heat casualty was no longer considered asignificant medical problem.

In the United States, heat casualties reached their maximumin 1943 and decreased thereafter. High monthly peak rates were encounteredduring the summers of the first 2 years, 12.49 per 1,000 per year in July of1942 and 11.15 per 1,000 per year in July 1943, but only slightly increasedyearly rates, 2.20 per 1,000 per year in 1942 and 2.79 per 1,000 per year in1943 (tables 41 and 42). The total yearly caseload of 5,852 in 1942 increased to14,470 in 1943, the highest figure of the war and indicative of the large numberof men in training. Deaths due to heat numbered 58 in 1942 and 111 in 1943. Thefollowing year (1944), the number of cases diminished to 4,299, the admissionrate fell to 1.08 per 1,000 per year, and the peakload during the summer monthsdropped to 3.82 per 1,000 per year (table 43). Deaths for the year numbered 23,and in 1945 with 2,315 cases, there were only 10 fatalities.

The reports from the Central and South Pacific and theSouthwest Pacific theaters were instructive. Except in some of the earlierisland campaigns, heat casualty was not a serious matter. Although thesetheaters became increasingly active in 1944 and 1945, they profited by theexperiences with heat casualty in the other hot theaters in the earlier years ofthe war. Thus, in the Southwest Pacific Area, the admission rate remained quiteuniform throughout the war, 1.72 per 1,000 per year in 1942, 2.03 per 1,000 peryear in 1943, and 1.97 per 1,000 per year in 1944, while the progressivelyincreasing number of cases-122, 386, and 1,061 for the 3 years respectively(tables 41, 42, and 43)-was again a reflection of the increase in the numberof troops.

In the last years of the war, most of the reports fromChina-Burma-India, the Southwest Pacific Area, and even the Middle East either donot mention ill effects of heat or indicate that heat casualty was not a medical

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problem of significance. The general opinion was thatalthough the efficiency of personnel was reduced there was little overtillness.

The reduction in heat casualty as the war progressed must beevaluated in terms of the progress of events in the various theaters. In sometheaters, the movement of troops out of hot areas may have accounted for thereduction in heat casualty; for example, in the United States where troopswere moved from training centers to oversea stations. However, similarreductions occurred in theaters where the number of troops remained unchangedwhile the demands on them increased; for example, in the Persian Gulf Command.Furthermore, low heat casualty rates persisted in still other theaters, such asthe Southwest Pacific, which became progressively more active. Theseobservations indicate that the reduction in heat casualties in the later yearsof the war was real.

These data lead to the implied conclusion that heat casualtyas a major problem is preventable under all circumstances in all hotenvironments. However, it must be considered that in the hottest areas onearth (Persian desert, lowland India, and Burma) military activity was concernedlargely with stable operations, such as supply and transportation, rather thanwith the less well regulated activity of combat. Most of the prolonged,large-scale combat was conducted in hot areas of somewhat lesser heat stress.Under these circumstances, it may be said that (1) relatively stableoperations were carried out with diminished heat casualty in the hottest areason earth and that (2) active large-scale combat was successfully waged in hotareas of somewhat lesser heat stress, where it was also possible to prevent alarge amount of heat casualty. Since large-scale combat was not conducted in thehottest areas, it is not known whether the available preventive measures againstheat casualty could have been effectively applied under such fluid and lessordered conditions.

CAUSE AND PREVENTION

The experience of the Armed Forces during World War II contains the answer to theproblem of living and working in hot climates.Why were adverse effects of heat prevalent in the early years of the war? Andwhy did they decrease toward the end of the war? It is the purpose of theremainder of this review to indicate themeasures responsible for reducing heat casualty.

A consideration of the military situation at the time theUnited States entered the war may serve as a background. The last half of1941 and the first half of 1942 saw much military activity in hot climates. The battlesin the African desert between the British and German Armies and the march of the Japanese through the junglesofSoutheast Asia and the islands of the Southwest Pacificfocused attention on the advantages to be gained by operations in legionspreviously considered impossible for com-

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bat because of climate. Moreover, the strength of the homefortresses of both Germany and Japan was considered so formidable thatcounterattack seemed most feasible from the periphery; that is, the recentlyconquered hot desert and jungle areas. Desert and jungle fighters were needed.However, there were many defects in our knowledge and experience of the peculiarstresses imposed by hot climates, of their deleterious effects, and of themeasures required to prevent heat casualty.

The factors which led to heat casualty, and the correctivemeasures taken to prevent such illness, were apparently much the same in allareas regardless of their location. This suggests that the same basic factorswere operating in the different areas, whether jungle or desert, and that theexperiences from all areas may be combined.

Acclimatization

For some time, it has been known that man must adapt himself(acclimatize) to a hot environment before he can perform physical work in thatenvironment effectively. The failure to appreciate the need for acclimatizationled some commanding officers to require men newly arrived from temperate intohot climates to perform hard work immediately.¹⁵ Inevitably, heat casualtiesresulted. In some areas, they were serious and numerous; in others, relativelymild to moderate. A majority of the cases of fatal heatstroke occurring in theArmy in the United States occurred in men who had been stationed in a hotenvironment for only a short period (a month or less).¹⁶Moreover, most of these fatalities occurred in men whooriginally came from the northern part of the United States. Lack ofacclimatization may also be considered an important factor in those heatcasualties which occurred during a sudden rise in temperature in more temperateareas.

The need for acclimatization was quickly learned. Wheneverpossible, troops newly arrived in hot climates were not at first required toperform a full day's work but were handled on programs of progressivelyincreased work until they were fully acclimatized. Heat casualties quicklydecreased, and troops were able to work hard in the heat without ill effects. Itwas generally felt that 1 month was required to attain full acclimatization,although considerable adaptation was attained in 4 or 5 days. The need ofacclimatization led to the realization that troops should be trained in climatessimilar to those in which they were ultimately to work or fight.

Laboratory studies on acclimatization to heat confirmed the observations in the field, clarified the physiological processes involved, and pro-

¹⁵Report, Armored Medical Research Laboratory, Fort Knox, Ky., 20 Oct. 1942, Project No. 2-8, Report on Results of Desert Field Study.
¹⁶Schickele, E.: Environment and Fatal Heat Stroke; An Analysis of 157 Cases Occurring in the Army in the U.S. During World War II. Mil. Surgeon 100: 235-256, March 1947.

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vided a sound basis for corrective measures.¹⁷ Thesestudies, conducted in hotrooms, revealed several pertinent facts. Hard work onfirst exposure to hot environments (both dry and humid) is never well toleratedand, if continued, leads to disability, no matter how excellent the generalphysical fitness. The unacclimatized man working in the heat manifests two majorundesirable phenomena which usually incapacitate him. He retains heat, with amarked rise in body temperature, and his circulation becomes deranged andunstable. Acclimatization is the development of physiological adaptation ofwhich the mechanism is not yet completely understood but which maintains thebody's thermal balance by increasing heat loss to meet the increased heatloads. This appears to be accomplished largely by the development of increasedevaporative cooling through more rapid and more copious sweating.¹⁸ Inturn, the deranged, unstable circulation of the unacclimatized state, associatedwith the heat retention, is avoided. Acclimatization begins with the firstexposure to heat and is attained most rapidly and completely by progressivelyincreasing the amount of daily work performed in the heat to the point ofcomfortable tolerance. The major portion of the adaptation is attained in from 4to 7 days and then progresses more slowly for 3 or 4 weeks. Physically fit menacclimatize more quickly than the unfit. On returning to a cool environment,acclimatization is retained well for 1 or 2 weeks after which it is lost atvariable rates. In some men, it is retained to an appreciable extent for as longas 1 to 2 months. The many factors which are detrimental to the well-being andperformance of men in the heat produce greater effects in unacclimatized than inacclimatized men.

Water

In the early days of the war, line officers believed in awater discipline, the two principal tenets of which were that drinking waterduring work in the heat is harmful and that men could be trained to work in theheat with progressively lower intakes of water. Their ideal was the "desertfighter" who could fight on "a pint of water a day." Such a manis a mythical figure,

¹⁷(1) Bean, W. B., and Eichna, L. W.:Performance inRelation to Environmental Temperature; Reactions of Normal Young Men toSimulated Desert Environment. Fed. Proc. 2: 144, 1943,(2) Eichna, L. W., Bean, W. B., Ashe, W. F., Jr., and Nelson, N.:Performance in Relation to Environmental Temperature; Reactions of Normal YoungMen to Hot Humid (Simulated Jungle) Environment. Bull. Johns Hopkins Hosp. 76:25-58, January 1945. (3) Taylor, H. L., Henschel, A. F., andKeys, A.: Cardiovascular Adjustments of Man in Rest and Work During Exposure toDry Heat. Am. J. Physiol. 139: 583-591, August 1943. (4) Henschel, A., Taylor,H. L., and Keys, A.: The Persistence of Heat Acclimatization in Man. Am. J.Physiol. 140: 321-325, December 1943. (5) Robinson, S., Turrell, E, S.,Belding, H. S., and Horvath, S. M.: Rapid Acclimatization to Work in HotClimates. Am. J. Physiol. 140: 168-176, November 1943. (6) Machle, W.: ThePhysiological Effects of High Temperatures. Mil. Surgeon, 95: 98-105, August1944.(7) Machle,W., and Hatch, T. F.: Heat: Man's Exchanges and Physiological Responses.Physiol. Rev. 27: 200-227, April 1947. (8) Taylor, C. L.: PhysicalExertion in the Heat; Some Notes on Its Physiology and Hygiene. J. AviationMed. 17: 137-145, April 1946.
¹⁸Report, Medical Department Field Research Laboratory,Fort Knox, Ky., 30 June 1947, Project No. 2-17-1, Thermal Regulation During Early Acclimatization to Work in a Hot Dry Environment.

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but the concept played a major role in producing heatcasualties, particularly in the United States, where unacclimatized andrelatively unfit men were suddenly required to undergo vigorous physicalexertion in hot environments with limited, and inadequate, intakes of water.Insufficient water also led to heat casualty in some of the earlier Pacificisland campaigns where men went ashore to perform strenuous activities withlimited water supplies which could not be augmented until the combat situationimproved. Medical officers in the field considered inadequate water intake andthe subsequent dehydration one of the most important factors leading to heatcasualty. In numerous reports,¹⁹ they pointed out the need for anadequate intake of water based not on preconceived ideas or hopes but on theactual needs of the men as determined physiologically by their water losses.

Studies in laboratory hotrooms²⁰andin the field²¹ quicklyproduced data which substantiated the recommendations of the medical officersin the field and disproved completely the possibility of training men to reducetheir water requirements. The huge water losses in sweat, approximately a literper hour for men working in the desert or jungle environment, continue whetheror not water is drunk and are only slightly reduced by dehydration. The sweatloss automatically sets the amount of water that must be replaced. Failure to doso leads to dehydration, with reduced blood volume, and predisposes todisability. It was repeatedly demonstrated that hardened, well-acclimatized men,who performed easily and well in the heat while drinking water as desired,either failed to complete the same amount of work or did so with greatdifficulty and marked inefficiency when on

¹⁹(1) Annual Report,87th Infantry Division, for 1943. (2) Annual Report, 99th Infantry Division, for1943. (3) Letter, Office of the Division Surgeon, Headquarters, 77th InfantryDivision, to Commanding General, 77th Infantry Division, 3 Aug. 1943, subject:Summary of Medical Experiences and Problems on Desert Maneuvers. (4) Sneidman,G. I.: Exhaustion and High Temperatures as Experienced in Desert Operations.[Professional paper.] (5) Annual Report, Persian Gulf Command, for 1944. (6)Annual Report, 113th General Hospital, for 1944. (7) Report,Headquarters, XIV Corps, to Commanding General, South Pacific, 3 June 1943,subject: Informal Report on Combat Operations. (8) Annual Report, 102d infantryDivision, for 1943. (9) Annual Report, 81st Infantry Division, for 1943. (10)Letter, Office of The Surgeon General, to Commanding General. Services ofSupply, 28 July 1942, subject: Heat Exhaustion and Fatigue. (11) Wallace, A.W.: Heat Exhaustion. Mil. Surgeon 93: 140-146,August 1943.
²⁰(1) See footnote 17 (1), (2), (6), (7), and(8), p. 212. (2) Pitts,G. C., Johnson, R. E., and Consolazio, F. C.: Work in the Heat as Affected byIntake of Water, Salt and Glucose. Am. J. Physiol. 142: 253-239, September 1944.
²¹(1) Adolph, E. F., Rahn, H., Gosselin, R. E., Goddard, D.R., Brown, A. H., Kelly, J. J., and Wolf, A. V.: Water Losses From Man in the Desert.Report No. 1,University of Rochester, Contract No. OEM-cmr 206, for Committee on MedicalResearch, Office of Scientific Research and Development, 20 Mar. 1943. (2)Rothstein, A., and Brown, A. H.: Water Requirements ofAir Force Personnel in the Desert During the Hot Season. Report No. 11,University of Rochester, Contract No. OEM-cmr 206, for Committee on MedicalResearch. Office of Scientific Research andDevelopment, 15 Oct. 1943. (3)Rothstein, A., and Gosselin, R, E.: Rates of Sweat Loss inthe Desert. Report No. 15, Universityof Rochester, Contract No. OEM-cmr 206, for Committee onMedical Research, Office of Scientific Research and Development, 30 Jan. 1944.(4) Adolph, E. F., Brown. A. H., Siple, P. A., and Heald, W. F.: SurvivalTime of Men Without Water in the Desert. Report No. 8, University of Rochester,Contract No. OEM-cmr 206, for Committee on Medical Research, Office ofScientific Research and Development, 23 May 1943. (3) Adolph, E. F., and Brown, A. H.: Economy ofDrinking Water in the Desert. Report No. 5, University of Rochester, Contract No.OEM-cmr 206, for Committee on Medical Research, Office of ScientificResearch and Development, 25 May 1943. (6) Adolph, E. F.: Water Shortage inthe Desert. Report No. 12, University of Rochester, Contract No, OEM-cmr 206,for Committee on Medical Research, Office of Scientific Research andDevelopment. 20 Oct. 1943.

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restricted water intakes. Furthermore, nothing is gained byfailing to replace the water losses as they occur. The total 24-hour waterintake was found to be just the same whether men drank as they desired, wheneverthirsty, or only at stated periods, such as mealtime. Withholding water untilstated drinking hours not only did not reduce the water intake but also led todehydration, with its discomfort and potentially serious consequences.

"Thirst quenchers" were shown to be of no value.²²They neither reduced the water requirement nor alleviated discomfort. Onlyone sound way of reducing the amount of drinking water was found; that is,wetting the clothing with nonpotable water.²³ The cooling effect ofevaporation of this water reduces the sweat output and conserves body water.

Quantitative studies based on observations in the field²⁴and in the laboratory²⁵ determinedthe water requirements for different rates of work in various types of hotclimates (table 50). When troops received amounts of water adequate to meetthese requirements, the incidence of heat casualty decreased sharply.²⁶

A byproduct of the quantitative studies was the prediction ofsurvival times in hot climates for men deprived of water and the formulation ofa sound plan of action for troops caught in such a predicament:

If men are isolated and have no hope of reaching water in afew hours they should as far as is feasible minimize their rate of water loss(1) obtaining maximalprotection from the sun, (2) remaining as inactive as possible, (3) usingwhat water they may

TABLE 50.-Water requirements forrepresentative types of work in hot climates, by type of activity

Activity	Illustrative duty	Water requirement1 in-
		Moderate temperatures2 (desert or jungle)	Severe temperatures3  (desert or jungle)
		Quart	Quart
Light	Desk work; guard; kitchen police	6	10
Moderate	Routine march on level; tank operation	7	11
Heavy	Forced marches; stevedoring; entrenching	9	13

¹Number of quarts calculated per man per day, for drinking purposes only.
²For desert, air temperature below 105? F.; for jungle, air temperature below85? F.
³For desert, air temperature above 105? F.; for jungle, air temperature above85? F.

Source: War Department Technical Bulletin (TB MED) 175, June 1945.

²²Wills, J. H.: Attempted Relief of Distress inDehydrated Men by Certain Drugs. Report No. 14, University of Rochester,Contract No. OEM-cmr 206, for Committee on Medical Research, Office ofScientific Research and Development, 24 Dec. 1943.
²³Lifson, N., and Visscher, M. B.: Effect of WetGarments on Body Weight Loss at High Environmental Temperatures. J. Indust. Hyg.& Toxicol. 25: 434-439, December 1943.
²⁴(1) See footnote 21 (1), (2), and (3), p. 213. (2) Adolph, E. F., andBrown, A. H.: Prediction of Water Requirements of Men in the Desert. Report No.7, University of Rochester, Contract No. OEM-cmr 206, for Committee onMedical Research, Office of Scientific Research and Development, 25 May 1943.
²⁵Report, Armored Medical Research Laboratory,Fort Knox, Ky., 20 May 1943, Project No. 2-6, Determination of Water andSalt Requirements for Desert Operations.
²⁶Circular Letter No. 119, Office of The SurgeonGeneral, Army Service Forces, 3 July 1943, subject: Acclimatization, Including Water and Salt Requirements of Troops in HotClimates.

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have in moderation and only after dehydration has proceeded for half a day since waterislost slightly more rapidly in early stages of dehydration than later, (4)confining any necessary exertion (walking toward water) to the cooler hours of the night, (5)seeing that no water they already have isspilled or wasted.²⁷

Since men are unable to walk after losing body water to theextent of 10 percent of their body weight, but may survive if rescued when theyhave lost body water to the extent of 20 percent of their body weight, thefollowing survival times at stated activity have been calculated: (1) At dailymean shade temperature below 70? F., 3 nights of walking can be accomplished (65miles); (2) at daily mean shade temperatures between 70? and 80? F., 2nights of walking can be completed (45 miles); and (3) with daily mean shadetemperature above 80? F., a man can walk only 1 night (25 miles). Also, if themean temperature is 95? F., a man reaches the limit of his walking ability in 1day, and at 120? F., in one-third of a day. The importance of limiting activityto the cooler hours of the night, when the water losses through sweating aresomewhat diminished, at once becomes apparent.

The importance of an adequate water intake in theprevention of heat casualty cannot be overstressed. Since it is physiologicallyimpossible to reduce the water losses in a hot environment, such losses must bereplaced.

Salt

The need for an adequate salt intake to replace the salt lostthrough sweating seems to have been better understood by line officers than theneed for water replacement. At times, this need was overemphasized, and saltreplacement was sometimes considered more important than water replacement. Insome instances, the serious mistake was made by considering that theadministration of added salt automatically took care of the water requirement.

Ill effects attributable solely to salt deficiency (heat cramps) were either absent, or infrequently encountered. Nevertheless, reports from hot theaters stated that inadequate salt intake played a significant part in the production of heat casualty and that casualties were salt deficient. Medical officers advocated the use of salt and noted beneficial effects as a result, not only in the reduction of heat casualty but also in the improved well-being and work efficiency of the men. Since so many reports recommended additional salt, its advantages cannot be discounted. However, one cannot overlook the fact that salt was usually taken with water and that the added water may have really been the more significant addition.

The intake of supplemental salt proved to be quite a problem.Compressed tablets of salt did notdissolve well and at times passed through the gastrointestinal tract onlypartially absorbed. Nausea and vomiting often resulted from their irritation ofthe stomach. These effects prejudiced the

²⁷See footnote 21 (4), p. 213.

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men against salt. Of greater importance was the risk offurther dehydration from loss of fluid in the vomitus and through thecurtailment of oral intake of fluids. In order to reduce gastric irritation,tablets with different fillers were tried. Sodium bicarbonate and glucose tendedto induce more rapid disintegration and solution of the tablet but did notremove the gastric irritation. Another approach was the use of a plastic fillerto retard the rate of solution of the tablet yet permit complete solution of thesalt within the insoluble plastic matrix. Perhaps the best method developed wasto dissolve the salt in water to make a final concentration of 0.1 percent salt-two10-grain salt tablets or one-fourth of a teaspoonful of salt to each quartcanteen of water.²⁵ Though brackish, such water is not unpleasant anda taste for it is quickly acquired. By the addition of colloids and flavors,such as are contained in milk and barley water for example, the orally toleratedsalt content of liquids can be increased up to 0.2 to 0.4 percent. Theseconcentrations are not often necessary. Finally, most of the salt requirementcan be supplied by salting the food more heavily, particularly the bland foods,such as potatoes and rice.

Controlled studies in the laboratory²⁹and in the field³⁰ provedthat water replacement is much more important, and critical, than saltreplacement and that deterioration in working efficiency and heat casualty willresult much more quickly when water is denied than when salt is withheld.Maximum work efficiency in the heat is maintained when water is replaced hour byhour; salt, day by day. Although efficiency and output of work fall when thesalt intake is inadequate, too much salt, or salt without water, produces notonly distressing subjective symptoms but also requires body water for itsexcretion and actually leads to a reduced work efficiency.

During acclimatization to heat, the body adapts to conservesalt by secreting a sweat low in salt content. This compensating mechanism ofthe sweat glands is very effective. When salt intake is reduced sharply, thesalt concentration in sweat becomes very low, permitting equilibrium on intakesas low as 3 grams daily even though the daily sweat output is from 6 to 8liters.³¹ The adrenal gland is suggested as the mediator of thismechanism.³²

²⁸See footnotes 25 and26, p. 214.
²⁹(1) See footnote20 (2), p. 213. (2) Taylor, H. L., Henschel, A., Mickelsen, O., and Keys, K.:The Effect of Sodium Chloride Intake on the WorkPerformanceof Man During Exposure to Dry Heat and Experimental Heat Exhaustion. Am. J. Physiol. 140:439-451,December 1943. (3) Johnson, R. E., Belding, H. S., Consolazio, F. C., and Pitts, G. C.: The Requirements of Water and of Sodium Chloride for the Best Performance of Men Working in Hot Climates. Report No. 13,Harvard Fatigue Laboratory, for the Committee on Medical Research, Office ofScientific Research and Development, 25 Sept. 1942.
³⁰(1) See footnote 21 (3), p. 213. (2) Adolph, E. F., Wolf,A. V., and Kelly, J. J.: Salt in Relation to WaterMetabolism in the Desert. Report No. 3, University of Rochester, Contract No.OEM-cmr 206, for the Committee on Medical Research, Office of ScientificResearch and Development, March 1943.
³¹(1) Conn, J. W., and Johnston, M. W.: Improvement ofAbility of Soldier to Work in Humid Heat. Report No. 18, Contract No. OEM-cmr 232, for the Committeeon Medical Research, Office of Scientific Research and Development, 1 Mar. 1944. (2) Conn, J. W., andJohnston, M. W.: Improvement of Ability of Soldier to Work in Humid Heat. Report No. 10, Contract No.OEM-cmr 232, for the Committee on Medical Research, Office of Scientific Research andDevelopment, 1 July 1944.
³²Conn, J. W., and Johnston, M. W.:Improvement in Ability of Soldier to Work in HumidHeat. Report No. 18, Contract No. OEM-cmr 232, for the Committee on MedicalResearch, Office of Scientific Research and Development, November 1945.

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As stated on page 212, sweat output increases duringacclimatization to heat. Because salt conserving mechanisms exist but waterconserving mechanisms do not, replacement of the salt is physiologically lessurgent than replacement of the water. Determinations of the chlorides in theblood and the urine of troops in the American desert area³³and in the urine oftroops on several of the Pacific islands³⁴ revealedno salt deficits in the men even after long sojourns in the hot climates.

Activity

Most heat casualties occurred during, or shortly aftercompletion of, strenuous physical activity, such as long or forced marches oftenwith heavy packs, close order drill, obstacle course runs, and various types offield exercises. Resting or lightly active men were rarely affected. Thus, ofthe 265 heat casualties treated by the Station Hospital, Fort Eustis, Va., from1 May 1943 through September 1943, none occurred on Sunday.³⁵

Physical activity as a causative factor in heat casualty wasclosely associated with the external temperature. Work which could be performedwithout difficulty in the cooler parts of the day led to heat casualty whenattempted in the midday hours. In all hot areas, medical officers quicklyrecommended decreased physical activity during the heat of the day. Scheduleswere revised and, where possible, the midday siesta became a part of the dailyroutine, even to being enforced in some areas. The early morning hours and thenights were utilized for work, and heat casualty diminished; often, work outputincreased and morale improved. For example, in the summer of 1944, the PersianGulf Command instituted daily rest periods from 1300 hours to 1700 hours, duringwhich vehicles were not driven across the desert, except in emergencies. Recordsfor the hauling of supplies were broken in July of that year (p. 208). Even incombat, military observers recommended that H-hour be as early as possible for"during the middle of the day the heat is so intense that troops makelittle progress."³⁶

After correlating the incidence of heat casualty in troops intraining with observed environmental temperatures, medical officers recommendedthat physical activity should be reduced when the environmental wet bulbtemperature reached 70? F. and that it should be halted for unseasoned

³³Rosenbaum, L.: Significance of Salt (NaCl) in TorridTemperatures. Mil. Surgeon 98: 43-47, January 1946.
³⁴(1) Report, Special Survey Team,to The Surgeon General, 22 Aug. 1945, subject: Nutrition Survey inPacific Theater of Operations. (2) Kark, R. M., Aiton, H. F., Pease, E. D.,Bean, W. B., Henderson, C. R., Johnson, R. E., and Richardson, L. M.: TropicalDeterioration and Nutrition. Clinical and Biochemical Observations on Troops.Medicine 26: 1-40, February 1947.
³⁵Borden, D. L., Waddill, J. F., Grier, G. S. III: StatisticalStudy of 265 Cases of Heat Disease. J.A.M.A. 128: 1200-1205, 25 Aug. 1945.
³⁶Report, to Commanding General,Army Forces, Army War College, 11 July 1944, subject: Observer Report on theMarianas Operation (FORAGER).

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troops when it reached 81? F.³⁷When activity inthe midday heat could not be discontinued, men were to be trained by graduallyincreasing their activity during the hot hours,³⁸and the loadsat these hours were to be as light as possible.

Removing the men from the midday sun also served to preventincapacitating sunburn. The harmful effects of solar actinic rays and the needfor gradually increasing exposure in order to avoid disabling sunburn had to beemphasized.

The relation between the maximum rate of efficient workpossible and the severity of environmental heat and humidity receivedconsiderable controlled laboratory study during the war.³⁹ Theproblem proved to be complex, and its full consideration is beyond the scope ofthis review. However, when the severity of the environment increased, the workrate possible without ill effects always decreased. The simplest index of theseverity of an environment for work proved to be the wet bulb temperature. Forfit men, fully acclimatized to both dry and moist heat, 92? F. was the upperlimit of wet bulb temperature at which they could march, in the nude, with a20-pound pack at 3 miles per hour for 4 consecutive hours (work expenditure, 250kilocalories per hour) without disability. When clothed in a single layer ofArmy fatigues of herringbone twill, the limiting wet bulb temperature wasreduced to 90? F.⁴⁰

The cooling power of the environment, also termed the"thermal acceptance of the environment" and defined as the amount ofheat which a given environment can remove from the body surface of a workingman,⁴¹ was also studied. If a man, by his work activity, produced moreheat than the environment could remove from his body surface, obviously his bodytemperature would rise and he became a candidate for heat casualty. On analysis, most of the deaths due to heatstroke(hyperpyrexia) in the Army stationed in the United States were found to haveoccurred where the "cooling power" of the environment was low, lessthan 500 Cal. per m.² per hr. (calories per square meter of bodysurface per hour); a small number occurred where it was between 500 and 600Cal. per m.² per hr.; and very

³⁷See footnote 35, p. 217.
³⁸See footnote 19 (10), p. 213.
³⁹(1) See footnote 3, p. 196; and footnote 17 (8), p. 212. (2)Eichna, L. W., Ashe, W. F., Jr., Bean, W. B., and Sheeley, W. B.: The Upper Limits of Environmental Heatand Humidity Tolerated by Acclimatized Men Working in Hot Environments. J.Indust. Hyg. & Toxicol. 27: 59-84, March1945. (3) Robinson, S., Turrell, E, S., and Gerking, S. D.: PhysiologicallyEquivalent Conditions of Air Temperature and Humidity. Am. J. Physiol. 143:21-32, January 1945.
⁴⁰Shelley, W. B., Eichna, L. W.,and Horvath, S. M.: The Effect of Clothing on the Ability of Men to Work inIntense Heat. J. Clin. Invest. 25: 437-446, May 1946.
⁴¹(1) Report, Climatology and Environmental Protection,Research and Development Branch, Military Planning Division, Office of theQuartermaster General, 25 Aug. 1944, subject: Conference on the Principles ofEnvironmental Stress on Soldiers for the Purpose of Developing a Climatic IndexSuitable for Mapping Purposes for the Protection of Troops Operating in AllClimates. (2) Report, Climatology and Environmental Protection, Research andDevelopment Branch, Military Planning Division, Office of the QuartermasterGeneral, 20 Aug. 1945, subject: Thermal Balance of theHuman Body and Its Application as an Index of Climatic Stress. (3) Report,Climatology and Environmental Protection, Research and Development Branch,Military Planning Division, Office of the Quartermaster General, 17Sept. 1945, subject: Thermal Acceptance Ratio.

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few, usually older obese soldiers, where the thermalacceptance of the environment exceeded 600 Cal. per m.² per hour.⁴²

Physical Fitness

A physically unfit man who is incapable of working intemperate climates at high levels of energy expenditure for as long as a fit manis at a much greater disadvantage in a hot environment. Lack of physical fitnesscontributed significantly to heat casualty in troops, chiefly in the UnitedStates. Mobilization suddenly subjected men to physical conditions requiringeffort far beyond that to which they were accustomed. In temperate climates,most recruits were able to tolerate such increased physical activity, althoughinability to carry on was not infrequent. In hot climates, heat plus theexertion required produced a total load exceeding the physiological capabilitiesof many men, and casualty resulted. Thus, fatal heat casualties were morefrequent in the United States than in any other theater. Furthermore, casualtieswere more frequent in men who were overweight, who were in the older age groups,and whose service in the Army had been of short (weeks to months) duration.Better physical fitness was believed to be an important factor in the lowerincidence of heat casualty in units in hot theaters overseas than while intraining in the United States.⁴³

Heat casualty rates fell when the physical conditioningprograms for recruits were guided by their performance and tolerance and whensuch programs were, at least initially, less accelerated in hot than intemperate environments. Good physical fitness does not, however, eliminate theneed for acclimatization. Controlled observations have amplydemonstrated that fit men also suffer disability on attempting hard work onfirst exposure to hot environments, although they acclimatize more rapidly thanunfit men and, when acclimatized, are capable of working more efficiently.⁴⁴

Sleep and Rest

Lack of sleep and rest in areas where high temperatures weresustained day and night predisposed to heat casualty. Men who worked on nightshifts and then attempted to sleep during the day in quarters where airtemperatures reached 120? to 135? F. (Iran) could not get adequate rest, andmore rapidly became heat casualties. A cool place to sleep is the bestpreventive of heat disease among personnel. Men can tolerate through the dayheat loads as great as any occurring naturally if they obtain adequate sleep and

⁴²See footnote 16, p. 211.
⁴³Pacific Warfare Board Report No. 60, U.S. Army Forces,Pacific, GHQ. 4 Sept. 1945, subject: Requirements of Tank Design and Operation in Relation toEffectiveness of Armored Personnel.
⁴⁴(1) Adolph E. F.: PhysiologicalFitness for the Desert. Fed. Proc. 2: 158-164, 1943. (2) Johnson, R. E., andRobinson, S.: Selection of Men for Physical Work in Hot Weather. Report No. 16,Harvard Fatigue Laboratory, Contract No. OEM-cmr 54, for the Committee onMedical Research, Office of Scientific Research and Development.

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if they have comfortable quarters in which to relax and restwhen not working.

Good housing in which men could sleep and relax, includingair-conditioned barracks for night crews, was instrumental in lowering heatcasualty rates in the Persian Gulf Command (p. 209). In desert areas, effectiveair conditioning was obtained by evaporative cooling, using simple "desertcoolers,"⁴⁵ boxes with 6-inch layers of excelsior over which water drippedslowly and, when obtainable, a fan blowing air over the box. Such devices wouldbe of no value in the humid Tropics. But whether in the desert or the Tropics,fans were recommended, since the additional air movement produced a coolingeffect.

Nutrition

In some hot areas, malnutrition apparently predisposed toheat casualty, particularly early in the war when much of the food was eitherpackaged (C- and K-rations) or so dehydrated that it was unpalatable. Strictwater rations made this food even less edible. Failure to eat led to loss ofweight and occasionally to mild avitaminosis. Recommendations were made forbetter food, for less packaged food (the necessary packaged food in a morepalatable and acceptable form), and for additional vitamins. As the rationsimproved, heat casualties decreased. Since, over the same period, more importantcorrective measures were also instituted, the role of improved nutrition in thereduced heat casualty rate cannot be evaluated. Medical officers in the fieldfelt that an inadequate diet rendered the men more susceptible to heat casualtyonly when it produced definite malnutrition.

Controlled studies revealed that no known food factor willprevent the ill effects of heat and that the dietary requirements of men in theheat are essentially similar to those in temperate climates. There is the sameneed for the maintenance of caloric balance.⁴⁶ The specificdynamic action of protein does not adversely affect the thermal equilibrium ofmen working in the heat.⁴⁷ Vitamin losses in the sweat arenegligible,⁴⁸ even for the water-soluble vitamins (thiamine andascorbic acid), and the vitamin requirements for work in the heat are notincreased. At one time, vitamin C was thought to increase work efficiency in theheat and to prevent heat exhaustion, but this was subsequently disproved.⁴⁹Additional carbohydrates, such as glucose, are not helpful. A nutritionsurvey, including biochemical

⁴⁵See footnotes 8 and 9, p. 206; and footnote 19(5), p. 213.
⁴⁶Johnson, R. E.: NutritionalStandards for Men in Tropical Climates. Gastroenterology 1: 832-840, September1943.
⁴⁷Pitts, G. C., Consolazio, F. C., and Johnson, R. E.:Dietary Protein and Physical Fitness in Temperate and Hot Environments. J.Nutrition 27: 497-508, June 1944.
⁴⁸(1) Sargent, F., Robinson, P.,and Johnson, R. E.: Water Soluble Vitamins in Sweat. J. Biol. Chem. 153: 285-294, April 1944.(2)Taylor, H. L.: Climate and Vitamin Requirements. Lancet 63: 358-359, November1943.
⁴⁹Henschel, A., Taylor, H. L.,Brozek, J., Mickelsen, O., and Keys, A.: Vitamin C and Ability to Work in HotEnvironments, Am. J. Trop. Med. 24: 259-265, July 1944.

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analyses of blood and urine of combat and garrison troops onseveral of the Pacific islands, revealed no deficiency of vitamins, protein, orhematopoietic factors in the men. Only occasional low values were found.

Overindulgence in alcohol led to heat casualty, but it is notpossible to determine if alcohol alone or the dissipation associated with itsuse was the causative factor.

Clothing

Heat casualty directly attributable to clothing was difficultto establish. Men wearing heavy clothing, relatively impervious to air, tightlyfitted over the body, with the closure of such ventilation ports as the trouserbottoms (by leggings), the sleeve openings (by wrist buttons), and the neck (byflaps and buttons), sustained an additional heat load. Many recommendations weremade for light clothing, permeable to air, loosely fitting, and whereverfeasible with neck, trouser bottoms, and sleeves open to permit greaterventilation of the body. These clothing specifications usually could not be metin the jungle climates, because of the necessity of covering as much of the bodysurface as possible and of closing all ventilation ports in order to avoid theinsect vectors of many of the tropical diseases (malaria, dengue, filariasis,and scrub typhus). By the war's end, the use of insecticides and insectrepellents suggested an avenue of investigation which might eventually permitthe wearing of loose clothing in the Tropics with reasonable safety.

Clothing is undesirable in hot climates because it interfereswith air movement over the body and thus hinders evaporative and convectivecooling, the extent of this interference depending upon the type of cloth andits fit. Several quantitative studies have determined the heat loads ofdifferent clothing in various environments.⁵⁰ Where the solar radiantheat is great and the evaporative gradient large, as in the desert, clothing isbeneficial since it reduces the radiant heat load more than it interferes withthe evaporation of sweat.⁵¹ Where both the radiant heat and theevaporative gradient are small, as in the Tropics, the net effect of clothing isharmful since it seriously hampers an important avenue of heat loss, evaporationof sweat and produces little benefit by reducing the already small radiant heatload.

Surgical operations in hot environments present serious difficulties. Extensive covering with sterile drapes greatly reduces heat elimination by patients. The administration of the usual preoperative atropine, by cur-

⁵⁰(1) Report, Armored Medical Research Laboratory, Fort Knox, Ky., 17 July 1945, Project No. T-5, Test of Flameproofed Clothing, Physiological Effects of Wearing Flameproofed Clothing in Hot Environments. (2) Report, Armored Medical Research Laboratory, Fort Knox, Ky., 24 Nov. 1943, Project No. 2 (2-3, 18). Test of Adequacy and Ranges of Use of Clothing for Jungle Operations. Effects of Impregnated and Impervious Clothing Upon Efficiency of Personnel. (3) Robinson, S.: Committee on Medical Research Interim Report No. 12 (Revised), Indiana University Medical School, 2 Nov. 1944.
⁵¹See footnote 21 (3),p. 213.

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tailing sweating, greatly aggravated this difficulty.Certainly, anhidrotic drugs are to be avoided in any hot environment since theyreduce evaporative cooling as an avenue of heat loss.

Previous and Associated Illnesses

Susceptibility to heat casualty was increased by intercurrentillness, no matter how mild; that is, venereal disease, upper respiratoryinfections, dysentery, overfatigue, constipation, immunizing inoculations,simple gastrointestinal disturbances, and diarrhea. The predisposing commondenominator in these disturbances mayhave been the associated increased water losses. Return to duty too soon afterrecovery from any previous illness similarly predisposed to heat casualty, andconvalescences had to be prolonged. Previous heat illnesses at times left menparticularly prone to subsequent attacks. Medical officers soon realized thatgreater care, often to relieving men from duty, was required for disturbanceswhich in temperate climates would have been unimportant.

Education

Indoctrination of each individual soldier for life in hotenvironments is essential to the avoidance of heat casualty. The war threw intothe hottest of climates large numbers of men who had neither knowledge norexperience of how to live in the heat and who had to learn all of theacclimatization principles just discussed. These principles were disseminatedthrough Circular Letters No. 119⁵² andNo. 136⁵³ from the Officeof The Surgeon General. These letters did much to remove preconceived anderroneous ideas, particularly concerning water and salt requirements andworkloads in the heat, factors which had led to most of the heat casualties.Beneficial results were quickly apparent. For example, a unit previouslyinstructed and prepared, and adhering to these principles, moved from a camp innorthern United States into the California desert and trained there withoutsignificant heat casualty.⁵⁴

TREATMENT

The war experience contributed no new principles or methodsto the treatment of heat casualty but provided a more complete evaluation ofpreviouslyutilized, or suggested, therapeutic measures. This is important bothbecause of the large number of men treated and because of the un-

⁵²See footnote 26, p. 214.
⁵³Circular Letter No. 136, Officeof The Surgeon General, Army Service Forces, 28July 1943, subject: Treatment of Heat Stroke, Heat Exhaustion and Heat Cramps.
⁵⁴Annual Report, 51st Evacuation Hospital, for 1943.

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complicated nature of the heat casualties. They occurred inhealthy young men, free from the associated, complicatingdiseases and disabilities so prevalent in civilian heat victims and so likely toconfuse the analysis of therapeutic measures.

It is not the purpose of this report to review the variousclinical types of heat casualty, but a brief description of the more important,or frequent, types of casualty encountered will be given. Heat cramp, due toloss of body salt, usually through sweating, is characterized by painfulcontractures of the voluntary muscles, especially of the abdominal wall; therectal temperature is normal. Ill-defined effects of heat include suchmanifestations as a sense of overheating, fatigue, headache, giddiness, and skinrashes in an afebrile subject who, though ill and exhausted, can still moveunder his own power. Heat exhaustion is largely a circulatory faultcharacterized by a lowered blood volume, resulting from water loss (sweating)without adequate water replenishment. The temperature is normal or moderatelyelevated (102? F.). There is severe exhaustion, a cool wet skin, anorexia (attimes with vomiting), giddiness, syncope (especially when erect), headache,evidence of dehydration, oliguria, and usually tachycardia. Hyperpyrexia(heatstroke) is characterized by a high rectal temperature, over 106? F.; byunconsciousness or delirium, often with convulsions; by circulatory collapsewith shock; and by a hot dry skin without sweating. It probably results from afailure of the mechanisms for heat loss. Although each of these categories maybe considered a separate clinical entity, not infrequently cases wereencountered which did not fit into the accepted classification but showedmanifestations of several categories; for example, "borderlinehyperpyrexia" which showed symptoms of both heat exhaustion andheatstroke. Furthermore, some patients progressed from one category toanother.

Mild cases.-The categoryof mild cases contains patients with ill-defined symptoms and those with heatexhaustion. The former required little more than rest, in as cool a place aspossible, water and possibly salt, by mouth, and observation. Improvement wasuniformly rapid, permitting return to quarters within several hours or the nextday.

Heat exhaustion was treated much the same way, but thepatients were usually hospitalized and treated longer andmore intensively. When vomiting interfered with the oral intake, intravenousinfusions of isotonic salt solution or of glucose in salt solution (2 to 3liters) were given until fluids by mouth were retained. Only occasionally werestimulants necessary. Improvement was usually rapid and recovery complete in aday or two. Adequate convalescence was essential before return to full duty.

Both types of mild cases were at times considerably worsewhen enthusiastic but uninformed aidmen administered salt (usually tablets) withlittle or no water.⁵⁵ Water is decidedly more important than salt forthese

⁵⁵See footnotes 29 (2) and (3)and 30 (2), p. 216.

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casualties, and salt alone is interdicted. Salt and watertogether constitute the optimal treatment.

The most important lesson learned from the mild heatcasualties was the realization that all heat casualties are potentially seriousand that the mildest of cases may deteriorate quickly and become dangerouslyill. Before this was appreciated, men who appeared only slightly ill werefrequently sent to their quarters (in some areas tents in which temperaturesreached 120? to 137? F.) only to be found several hours later seriously illand even comatose.⁵⁶ Others would suddenly, and unaccountably, becomecritically ill, even while awaiting attention in busy aid stations or hospitalwaiting rooms.⁵⁷ Again, men who appeared only mildly ill wouldcollapse while being transported in trucks to hospitals at a distance and uponarrival would be in a serious condition.⁵⁸ Heat casualty necessitatedprompt "on the spot" and continued attention, and men sent to quartersrequired repeated checking just as well as those in hospitals.

Severe cases.-The category of severe cases containspatients with hyperpyrexia (heatstroke) and those with the more serious of theso-called borderline hyperpyrexias. Only the treatment of hyperpyrexia isdiscussed here; the treatment of borderline hyperpyrexia became anindividualized intermediate regimen based upon the treatment schedules of mildand severe cases.

Treatment facilities.-Hyperpyrexia proved to be a truemedical emergency.⁵⁹ The high body temperature (107? to 112? F.),the cerebral disturbances of delirium, unconsciousness, and convulsions, and thecirculatory shock required prompt, accurate diagnosis and quick, energetictreatment. Proper treatment could be instituted only by organizing in advancethe required facilities and the trained personnel. Medical units in hot climatesestablished heat casualty treatment centers consisting of treatment rooms, airconditioned when possible, which were provided with a plentiful supply of thecoldest water available and equipped with sprays, fans, and special webbedtreatment tables to provide access of air to the greatest possible skin surface.Some centers provided tubs for ice water baths. Well-ventilated, and wherepossible air-conditioned, wards were set aside for convalescence. In the desert,the air conditioning was easily obtained by desert coolers, already described;in the Tropics, air conditioning was virtually unobtainable. The treatmentcenters were staffed by trained teams prepared for immediate action. Suchpreparations played a very important part in the reduction of mortality due toheat casualty.

Reduction of body temperature.-Rapid loweringof the body temperature was the first, and the most important, factor in thetreatment of

⁵⁶See footnote 19 (5), p. 213.
⁵⁷See footnote 19 (4), p. 213.
⁵⁸Nayer, H. R.: Letter to the Editor, Journal, AmericanMedical Association. J.A.M.A. 129: 1123, 15 Dec. 1945.
⁵⁹(1) Annual Report, Station Hospital, Fort Eustis, Va., for 1943. (2) See footnote 35, p. 217.

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hyperpyrexia.⁶⁰ The goal most frequently set wasto lower the rectal temperature to 102? F. within 1 hour. Two approaches wereutilized: (1) Evaporative cooling-wetting the patientcompletely and repeatedly with sprays of water and promoting evaporation of thewater by fanning, and (2) conductive cooling-immersing the patient in a tub ofcold water, containing ice when possible, and vigorously massaging the bodywhile it was thus immersed.

There has been a long argument between the advocates of thesetwo schools of treatment. Contention has centered about two points: (1) Whetherice or very cold water causes peripheral vasoconstriction which prevents bloodfrom reaching the skin and thus hinders cooling and (2) whether evaporation ofwater is a more effective method of removing heat than the melting of ice andthe subsequent heating of the cold water. From a physiological standpoint, thereasoning on these two points is as follows: Iced water can lower the skin temperature almost to zero,evaporation cannot lower it below the wet bulb temperatureof the environment (70? to 80? F.). If there is no interference with thecirculation of the blood through the skin, it follows that per unit time icewater will remove more heat from the blood perfusing theskin than will the evaporation of water from the skin. If,however, the cold water causes peripheral vasoconstriction, body cooling will behindered. Accumulating evidence of successful and rapid loweringof high body temperature by the use of ice water suggests that, atthe high body temperatures of heatstroke, undesirable peripheralvasoconstriction may not occur, particularly if the body is massaged. Therefore,rapid reduction in body temperature can be achieved.⁶¹In regard to the amounts of heat removed by the evaporation of water and bythe melting of ice, it is true that evaporation of water removes more heat thanthe melting of ice per unit mass of each. However, such an argument has force onlyfor equal amounts (masses) of the two agents and does not apply where amplesupplies of each are available to keep the body exposed to the lowesttemperature each agent can produce. Furthermore, in humid hot environments,evaporation is bound to be slow and, therefore, cooling inefficient.

On the basis of the evidence and reasoning justpresented,⁶² plus the accumulating experience from the field,the Army adopted, as the therapeutic procedure of choice for hyperpyrexia, thetotal immersion of the subject in cold, preferably iced,water with continuous massage of the body during theimmersion.⁶³ When ice is not available, the water must bechanged

⁶⁰(1) See footnote 9,p. 206; footnote 19 (4) and (5), p. 213; and footnote 35, p. 217. (2) Annual Report,19th Field Hospital, for 1944. (3) Letter, Maj. John T. Larkin, MC, toThe Surgeon General, 20 July 1945, subject: TB Med 175.
⁶¹Ferris, E. B., Jr., Blankenhorn, M. A., Robinson, H. W., and Cullen, G. E.: Heat Stroke; Clinical and Chemical Observations on 44 Cases. J. Clin. Invest. 17: 249-262, May 1938.
⁶²Conference on Adverse Effects ofHeat, Clinical Investigation Report No. 61, National Research Council, 3 Apr.1945.
⁶³War Department Technical Bulletin (TB MED) 175, June 1945,subject: Prevention and Treatment of Adverse Effects of Heat.

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often, or running water used. When water supplies are short,such expenditure may not be possible, and then evaporative cooling must beutilized. Since the effectiveness of evaporation depends on the velocity ofairflow over the body, fanning becomes essential. Evaporative cooling was foundmost effective when the patient was nude, but one medical officer reported thatcooling was most rapid from the completely wetted, clothed patient, presumablybecause of the increased surface area for cooling provided by the clothing.

Care was taken not to lower the rectal temperature too far,usually not below 102? F., although in one report no ill effects attended thelowering of temperature to between 99? and 100? F. Repeated checking of therectal temperature at 10- to 15-minute intervals was considered necessary tocontrol the period of rapid cooling. Thereafter, temperatures were taken at30-minute intervals until they had stabilized below 102? F., for 6 to 8 hours.Repeated readings were necessary to detect the not infrequent return of bodytemperatures to high levels. When hyperthermia recurred, the cooling treatmentwas repeated.

Central nervous system effects.-Next in importance tolowering the body temperature was the treatment of the associated centralnervous system effects. Of these, convulsions, often repeated, required promptattention. Besides their usual undesirable effects, convulsions produceadditional heat. Pentothal sodium (thiopental sodium) administered intravenouslyproved an effective therapeutic agent. Delirium and restlessness requiredtreatment, usually with other, milder, sedatives, such as barbiturates andparaldehyde. For deep coma, stimulants were used, but usually in associationwith treatment of circulatory shock.

Parenteral fluids.-The cessation of sweating which occursin hyperpyrexia usually prevents excessive fluid loss and dehydration, unlessthe latter is present before the onset of the heatstroke; for example, heatexhaustion progressing into hyperpyrexia. Although most patients withhyperpyrexia are not dehydrated, certainly not markedly so, the administrationof fluid by all available routes was recommended. Intravenous infusions ofisotonic salt solution, glucose, and particularly glucose in isotonic saltsolutions were commonly used. The amount of fluid administered was governed byits need, overadministration being avoided. As treatment producedfavorable results, fluids by mouth replaced the parenteral route.

Circulatory shock.-In the most severe hyperpyrexias,peripheral circulatory collapse with shock was commonly present. Thesepatients were particularly prone to develop pulmonary edema (perhaps aided bytoo vigorous parenteral fluid therapy), of which death was the likely outcome.The treatment of the shock was the same as for any other circulatory shock ofmedical origin-and usually as unsuccessful. Plasma was given intravenously,500 ml. at first and repeated after 30 to 45 minutes if there was noimprovement. Various circulatory stimulants, such as Coramine

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(nikethamide), caffeine, sodium benzoate, ephedrine, andMetrazol (leptazol), were tried, usually without benefit. When pulmonary edemadeveloped, inhalations of 100 percent oxygen and even venesection were employed,but atropine was specifically interdicted. The presence, or the development, ofshock was of poor prognostic import.

Antibiotic medication.-In some instances, penicillin andthe sulfonamides were administered on the possibility that some infectionsensitive to these drugs was present in a masked form and contributing to thehyperpyrexia. This must always be considered in patients with hyperpyrexiafor even a mild disease may be an important contributing factor. In otherinstances, heat casualties turned out to be severe cases of some other diseaseand required appropriate specific therapy. Proper diagnosis was especiallyimportant in those areas where severe and relatively unfamiliar diseasesproduced clinical pictures similar to heatstroke; for example, malaria. In someareas, an immediate malarial smear became a routine diagnostic procedure for allheatstrokes with the result that "on quite a few occasions the positivemalarial smear cleared the picture * * *."⁶⁴

Convalescence.-Following recovery from hyperpyrexia, longconvalescences were the rule, at first in air-conditioned surroundings ifpossible. A too rapid return to duty frequently led only to a repetition ofheat casualty. Since a number of these patients become sensitive to heat, theability of convalescents to work in the heat should be tested under medicalsupervision before they are returned to full duty.

DETERIORATION DUE TO HEAT

The acute, casualty-producing effects of heat thus fardiscussed constituted but one phase of the heat casualty problem in hotclimates. After men had learned to live in the heat so as to avoid acutecasualty, there still remained the problem of the deleterious effects ofprolonged stay in hot climates, generally believed to be a physical,physiological, and mental deterioration. Such deterioration is particularlylikely where high temperatures are maintained during both the night and the dayand throughout the year (Tropics) and less likely where there are seasonalvariations in temperature with, in season, exceedingly hot days but usuallycool nights (most deserts).

Deterioration did not occur in troops stationed in the hotareas of the United States since they never remained there long enough. Indesert areas overseas, troops in the Persian Gulf Command definitely"slowed down" in the hot months, with a drop in morale and efficiency,but were not considered deteriorated since they still performed well understress. The lassitude during the hot summer cleared quickly with the onset ofcooler weather. Although some officers felt that both mental and physicaldeterioration due

⁶⁴See footnote 19 (6), p. 213.

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to heat had appeared in some troops, the general opinion was that no realdeteriorationhad occurred, even in troops who had been in this hot desert for2 or 3 years.⁶⁵

For the Tropics, the available data do not afford a definite answer. Onesurvey specifically designed to study tropical deterioration indicated that,even after almost 4 years in the Southwest Pacific Area, troops remainedphysically fit and capable of performing hard work effectively.⁶⁶Nevertheless, there was a widespread feeling that the enervating effects of thehot climate "slowed the men down" and that "some reduction inefficiency in the absence of any disease seems unavoidable over a long period oftime." The terms "loss of efficiency" and"deterioration" were used to cover a variety of manifestations notedin troops long in the Tropics; for example, lessened interest, lessened physicalability to perform at levels of ordinary capacity,increased irritability, lethargy, and lowered reserve stamina. Although thesemanifestations are not usually considered casualty producing, neverthelessthey lowered the full efficiency of the commands and, in that sense, produce thesame result as overt casualties. These "deteriorative" changes wereusually noted after 8 to 12 months in the Tropics, while the first 2 to 4months, after attaining acclimatization, were considered the period of maximumefficiency.

It is difficult to evaluate properly the "slowing down" and"loss of vigor" of troops long in the Tropics. The changes were notovert or marked and, on demand, work was still performed effectively. It was notpossible to determine whether these changes were the result of true physical andphysiological deterioration induced by the hot climate or the result of mentaldeterioration and lack of motivation of men too long in any undesirablesurroundings regardless of climate. Controlled observations on troops in theSouthwest Pacific Area suggested that there was no tropical deterioration as aspecific entity differing from the deterioration in troops stationed elsewhereunder similar circumstances, except for climate. Certainly, the monotony of thehot, humid climate and of the work, the lack of recreation, and the absence oflong-accustomed amenities of life removed much, if not all, of the stimulus toexertion. The prevalence of skin disorders and tropical diseases constitutedan added physical and mental drain. Thus, it is not possible to state whethertrue climatic deterioration, physiological or mental, or both, was present inthese troops. Some loss of efficiency, whatever its origin, was present, butmild in degree and not limiting. Performance on demand, as in combat, was alwayshigh; when the demand relaxed, as in garrison duty, performance deteriorated.More careful observation and quantitative studies on troops in the Tropics arenecessary to clarify the problem of climatic deterioration. Until this isaccomplished, service of troops in the Tropics might well be limited to periodsof 1 to 2 years, as suggested by commanding officers in these areas.

⁶⁵See footnote 60 (2), p. 225.
⁶⁶See footnote 34, p. 217.

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HYPOHIDROSIS SYNDROME

Out of the war experience came the description of the hypohidrosis syndrome,a new clinical syndrome to be added to the ill effects of heat. Described in 8soldiers in the American desert,⁶⁷in 18 soldiers inAssam,⁶⁸ and in a similar though milder form in British troopsin southern Iraq,⁶⁹ the manifestations of thermogenic anhidrosis orthe hypohidrosis syndrome do not permit its inclusion inthe standard classification of heat casualty. Isolatedcases were also encountered in troops in Louisiana⁷⁰andin sailors in the Southwest Pacific.⁷¹

The essential features of this syndrome are (1) absence of sweating over mostof the skin surface; (2) retention of sweating in profuseamounts in various limited areas (usually the face andthen, in descending order, the axilla, the presternal area, and theinterscapular area); (3) relatively mild and indefinite symptoms ofoverheating, weakness, dizziness, and headache; (4) diuresis; and (5)nondescript cutaneous changes from prickly heat and transient papules in somecases to a dry skin with fine branny desquamationin most instances. These changes were either sudden or gradual in onset. Thesyndrome occurred in men who had been in a hot area for some time and usuallytoward the close of a hot season. Most of the men hadalways sweated profusely and some noted episodes of particularly profusesweating shortly before its cessation. All were aware that sweating hadstopped and that the urine output had increased. Mild, indefinite subjectivediscomfort for several days preceded the seeking of medical care. Usually, thepatients were not very ill and none had hyperpyrexia. Laboratory determinationshave been few, but no abnormalities in blood chloride, calcium, phosphorus,blood count, or glucose tolerance were found in limited studies. The few skinbiopsies examined did not show significant pathological changesin the sweat glands.⁷² On conservative treatment of rest in a coolplace, recovery from subjective symptoms was usually rapid, and sweatingreturned spontaneously over periods varying from several weeks to several

⁶⁷Wolkin, J., Goodman, J. I., and Kelley, W. E.:Failure of the Sweat Mechanism in the Desert; Thermogenic Anhidrosis. J.A.M.A.124: 478-482, 19 Feb. 1944.
⁶⁸Essential Technical Medical Data, U.S. ArmyForces, China-Burma-India, for April 1945, dated 10 May 1945, with enclosureNo. 1, subject: Hypohidrosis Syndrome-Report of Cases Seen at the 20thGeneral Hospital, 18 Mar. 1945.
⁶⁹LadeIl, W. S. S., Waterlow, J. C., and Hudson, M. F.: Desert Climate.Physiological and Clinical Observations. Lancet 2: 491, 14 Oct. 1944, and 527,21 Oct. 1944.
⁷⁰Blank, H.: Letter to the Editor, Journal,American Medical Association. J.A.M.A. 124: 1153, 15 Apr. 1944.
⁷¹Novy, F. G., Jr., and Ramsey, J. H.: Letter to theEditor, Journal, American Medical Association. J.A.M.A. 125: 738, 8 July 1944.
⁷²(1) See footnote 68, above. (2) Postwar observations have established thatthe hypohidrosis syndrome results from the closure of sweat pores, usually bykeratin plugs in the ostia of the sweat ducts. The surrounding areas arehyperkeratotic, but the walls of the sweat ducts remain intact. Sweat continuesto be formed by the gland but is reabsorbed from the occluded duct and overtsweating does not occur. This sequence of changes accounts for the frequentcutaneous manifestations associated with the syndrome, the patchy nature of theanhidrotic areas, and the return of sweating with conservative therapy.

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months.⁷³ In a few instances, large anhidrotic areas persisted foras long as 4 months. Followup studies, particularly on reexposure to externalthermal stress, are not available.

The reason for the cessation of sweating is as yet unknown. The present belief inclines toward a functional rather than a pathological etiology, to a "fatigue" or "exhaustion" of the sweat mechanism without defining whether such fatigue is central (neurogenic) or peripheral (sweat gland) in origin.

In connection with this syndrome, it is of interest that approximately 15percent of the racehorses imported from England and Ireland and raced inTrinidad, British West Indies, develop anhidrosois.⁷⁴ Their performance suffersand the horses are removed from racing. In contrast to the laboratoryfindings in the hypohidrosis syndrome in man, these horses have a lowered bloodchloride. When they are retired and turned out to pasture, there is aspontaneous recovery of their sweating mechanism associated witha return of the blood chloride to normal values. Anhidrosis has not beenencountered in native horses or crossbreeds.

CONCLUSION

The experience of the Armed Forces in hot climates during World War II (andthe almost identical experience of British troops)⁷⁵ contains the solution ofthe problem of living and working efficiently and effectively in hot climates.The answer was learned at the expense of a goodly numberof casualties and a fair number of deaths. The underlyingprinciples should not be forgotten but should form a basisfor the proper handling of troops in hot climates infuture years. That man possesses physiological mechanisms which permit him toadapt to heat and that adherence to sound physiologicalprinciples will permit him to work hard, efficiently, and effectively in anynaturally occurring hot environment can be concluded from thiswar experience. In closed spaces and in vehicles where the environment approachesor exceeds the physiologically tolerable upper limits of heat, coolingmethods must be provided. The essential features of this review have beenincorporated in War Department Technical Bulletin (TB MED) 175, June 1945,⁷⁶which is available for the lines of command as a basisof procedure in hot climates.

⁷³Hyman, A B.: Some Histopathologic Aspects of Disturbances of Sweating. A.M.A. Arch. Dermat. 66: 145-151, August 1952.
⁷⁴Special report, R. T. Gaylor, subject:Chronic Anhidrosis With Lowered Blood Chlorides in Race Horses at Trinidad, B.W.I.
⁷⁵(1) MacLean, K. A.: Observations on Sunstroke and Heat Exhaustion in Tropics. J. Roy. Nav. M. Serv. 29: 31-36, January 1943. (2) Morton, T. C.: Heat Effects inBritish Service Personnel in Iraq. Tr. Roy. Soc. Trop. Med. & Hyg. 37: 347-372, May 1944. (3) Palmer, H. A.:Case Report of Psychosis Following Heat Stroke. J. Roy. Army M. Corps 82: 186-189, April 1944. (4) Croom, J.H.: Effects of Heat; Account of Group of Cases Admitted to a General Hospital on Arrival in the Middle East.J. Roy. Army M. Corps 83: 288-292, December 1944. (5) Sheperd, H. M. D.: Effects of Heat in Iraq. J. Roy. Army M. Corps 84: 1-8, January 1945. (6) Critchley, M.: Problems of Naval Warfare Under Climatic Extremes. Brit. M.J. 2: 145, 4 Aug. 1945; 173, 11 Aug. 1945; and 208, 18 Aug 1945. (Croonian Lectures.)(7) Stenning, J. C.: Salt Deficiency States in Tropical Climate. J. Roy. Nav. M. Serv. 31: 129-146,July 1945.
⁷⁶Superseded by TB MED 175, 7 Aug. 1957.

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