426 THE RESPIRATION 



fail, partly because of the tendency of the body to suppress the activity of the metabolic 

 processes, so as to keep down heat production, and partly, no doubt, because the di- 

 gestive processes are working below par on account of there being less blood circulating 

 through the visceral blood vessels, it having been sent to the surface of the body to 

 be cooled off. The worker therefore tends to take less food, his metabolism becomes 

 depressed, and his factors of safety against bacterial infections become lessened. 



The risk of the appearance of symptoms on decompression is also greater when the 

 air in the caisson has been moist and hot, for the heart has been overworking to main- 

 tain the bloodflow in the dilated vessels; it gets fatigued and is consequently unable 

 to maintain, during decompression, a rate of bloodflow that is adequate for carrying 

 the gas-saturated blood to the lungs, where the excess of gas becomes dissipated. 



The criterion of proper working conditions in the caisson is therefore the wet-bulb 

 temperature. This should stand below 75 F. To maintain this condition it is necessary 

 to ventilate the caisson, preferably with air that has been cooled by cold-water radiators ; 

 ir any case, the ventilation should be adequate to keep down the wet-bulb temperature. 

 The increased expense of ventilation with cooled air would soon be balanced by the 

 greater working efficiency of the men. Constant circulation of the air in the caissons 

 by means of fans assists also in improving the conditions, for it helps to increase 

 dissipation of heat from the body. 



