3o6 RESPIRATION 



least io° below 88° in still air. With the ordinary clothing of 

 temperate climates the critical wet-bulb temperature is much 

 lower than without clothing, especially during muscular work. On 

 the other hand, with the air in motion, the critical wet-bulb tem- 

 perature is higher. The beneficial effects of fans, punkahs, etc., 

 during heat is well known. With the wet-bulb temperature above 

 the body temperature, however, the rise of body temperature is the 

 more rapid the more the air is in motion. 



In the climate of Great Britain the wet-bulb shade temperature 

 very seldom rises above 70°, even on very warm summer after- 

 noons ; but during heat waves in America a wet-bulb temperature 

 of 75° is not infrequently reached, and cases of hyperpyrexia 

 from the heat then become common. W^et-bulb temperatures of 

 over 80° are of course common in tropical countries, and are met 

 by proper adaptation of clothing and mode of life ; but the 

 amount of muscular exertion which is possible with a wet-bulb 

 temperature over 80°, except in a good breeze, is limited. In 

 ordinary rooms in a temperate climate, and when ordinary cloth- 

 ing is worn, a wet-bulb temperature of even 65° becomes oppres- 

 sive and likely to cause fainting and headaches in persons not 

 accustomed to heat or heavy muscular exertion. 



In order to obtain a simultaneous measure of the cooling action 

 on the body of air temperature, movement of air, and maximum 

 evaporation from the skin. Dr. Leonard Hill has devised an in- 

 strument known as the katathermometer. This consists of an 

 alcohol thermometer with a very large bulb, which, when an ob- 

 servation has to be made, is heated to about ioo°F. The flask is 

 jacketed with an absorbent jacket which can be moistened with 

 water. By the rate at which the water cools, a comparative esti- 

 mate can be obtained of the maximum possible combined cooling 

 action on the human body of movement of air, temperature, and 

 evaporation. The actual cooling effect of the air depends, of 

 course, on the physiological responses of the body, but cannot ex- 

 ceed the maximum shown by the wet katathermometer. 



The physiology of temperature regulation lies outside the scope 

 of this book ; but temperature effects are so liable to be confused 

 with effects due to chemical impurities in air that it seemed 

 necessary to refer briefly to the physiological disturbances due to 

 warm air. 



The air of occupied rooms is liable to be contaminated by 

 escapes of lighting gas; and under certain circumstances fatal or 

 very serious accidents from this cause may occur and lighting 



