ANIMALS THAT LIVE WITHOUT WATER l6l 



the excretion of waste products. The figure of 300 cc. 

 per day may be taken as the extreme minimal urine out- 

 put even on a protein-free diet. In soldiers engaged in 

 routine military activities but allowed all the water they 

 wanted to drink, urine formation averaged only 935 cc. 

 per day— a figure to be compared with 5900 cc. (6.2 

 quarts) of total water ingested by these same individ- 

 uals. It seems that even when men can drink all the wa- 

 ter they want, if sweating excessively they remain in a 

 shghtly dehydrated state, presumably because a con- 

 tinuing small water deficit in the body is necessary to 

 stimulate the drinking of the large quantities of water 

 that are necessary to compensate for the great loss in 

 sweat. In short, it is something of an effort to drink wa- 

 ter aU the time. 



The excretion of urine can be further reduced only 

 as the quantity of urinary solutes is reduced by diet, but 

 dieting, in turn, has very limited possibilities. Restriction 

 of salt intake is inadvisable because, even after adapta- 

 tion to heat, considerable salt is still lost by sweat, and 

 salt restriction can lead to salt deficiency with serious 

 clinical disturbances. Protein intake can be moderately 

 restricted, but if there is too httle protein in the diet nu- 

 trition will be impaired. In any case, the fraction of water 

 lost in the urine (700 to 900 cc.) as compared with sweat 

 (7000 cc. and upwards) is so small that such measures 

 are of no practical advantage. 



It is believed that men who suffer near-lethal de- 

 hydration cease to form urine, probably as a result of 

 circulatory failure and consequent reduction in blood 

 pressure and hence in the filtration rate. There is as yet 

 no evidence that the filtration rate in man can be func- 

 tionally reduced in order to conserve either salt or water, 

 short of the inevitable reduction in renal blood flow that 

 follows when circulatory failure leads to vasoconstriction 

 throughout the body in order to preserve the blood sup- 

 ply to the heart and brain. Man in partictdar, and proba- 

 bly the majority of mammals, thus differ from the 



