298 



TEMPERATURE AND HUMIDITY 



the body to produce certain stated amounts 

 of sweat (500, 700, and 900 grams per hour) . 

 At a temperature of 27°C both resting and 

 working subjects can adjust in still air even 

 at 100 percent relative humidity. The rest- 

 ing subject can also adjust with any relative 

 humidity at 32°C and the resting subject in 

 rapidly moving air (100 feet per minute) can 

 adjust with any humidity up to 35°C. The 

 general slope of the lines below these points 



39°C and 20 percent relative humidity, and 

 to 43°C and 3 percent relative humidity. 

 In this area, however, the other limiting fac- 

 tor, the power of the body to produce sweat, 

 comes into the picture. In this respect indi- 

 viduals vary widely; and the same individual 

 may greatly increase his ability to secrete 

 sweat. Dill (11) has shown that a subject 

 working in hot dry desert air can double his 

 capacity for moisture production, by prac- 



100 



90 



»- 



u 80 

 <J 

 a. 

 u 70 

 a 



60 — 



5 50 — 



5 



J 40 



^ 30 



< 20 



_j 

 u 

 a. 10 



DRY BULB TEMPERATURE 



Fig. 8. Upper limits of evaporative regulation. Curve A, working; heat production 425 Cal. per 

 hour, air movement ISfpm; Curve B, resting; 85 Cal. per hour, air movement 15 fpm: Curve C, resting; 

 85 Cal. per hour, air movement 100 fpm. Crosses indicate points on limits which can be reached through 

 the indicated evaporative water loss in grams per hour. 



indicates the limits of possible adjustment 

 based on the absorptive capacity of the at- 

 mosphere. The resting nude can, of course, 

 adapt to much more extreme conditions than 

 the w^orking subject, and the zone of adapta- 

 tion is further broadened by a high degree of 

 air movement (100 feet per minute). 



In Line A of Fig. 8, it will be noted that 

 at 32°C the upper limit for the working sub- 

 ject is at 55 percent relative humidity; if this 

 line were continued downward and to the 

 right on a basis of atmospheric absorptive 

 power, the working subject would adjust to 



tice, from 600 grams to 1200 grams per hour 

 (from a little over a pint of water to a little 

 more than a quart) . In football games even 

 higher figures have been recorded. If, how- 

 ever, we assume a representative figure for 

 the normal individual, approximating Dill's 

 initial value, it is found that above 32°C the 

 working subject would not be able to produce 

 the amount of moisture necessary for adjust- 

 ment, even though the atmosphere could 

 absorb it. For the working subject pro- 

 ducing 700 grams of moisture, this limit of 

 secreting power would come at 39°C, and for 



