101 



during the hottest hours of day remain in their burrows where the air 

 is more nearly saturated with moisture and evaporation is relatively 

 small." (Pp. 175-176) : "An application of these principles would 

 undoubtedly serve to prolong life, when suitable water for drinking 

 is not available. In such cases the food should consist of carbohy- 

 drates and fats. Proteins should not be used The water re- 

 quired for preventing uremic poisoning under these conditions is small 

 and if the relative humidity of the surrounding air is high enough to 

 prevent rapid evaporation of water from the body, the metabolic water 

 arising from the oxidation of nutrients may be ample for the purpose." 

 (Page 181) : "Metabolic water derived from the oxidation of organic 

 nutrients would probably be sufficient for all animal needs were it not 

 for the elimination of poisonous substances resulting from protein de- 

 generation." 



The preceding cjuotation brings out very clearly the harmful effects 

 of an accumulation of uric acid upon the animal. This is only a special 

 case illustrating a general law, for except water the main end products 

 of metabolism are acid. There is thus a constant tendency for acid to 

 accumulate, as Henderson ('13a: 158-159; see also '13b) has said: 

 "This tendency toward acidity of reaction and the accumulation of acid 

 in the body is one of the inevitable characteristics of metabolism; the 

 constant resistance of the organism one of the fundamental regulatory 

 processes. Now it comes about through the carbonate equilbrium that 

 the stronger acids, as soon as they are formed, and wherever they are 

 formed, normally find an ample supply of bicarbonates at their dis- 

 posal, and accordingly react as follows .... The free carbonic acid 

 then passes out through the lungs, and the salt is excreted in the urine." 



Recently Shelford ('13b, see also '14a) has summarized the phys- 

 iological effects of water-loss by evaporation and other methods. It 

 is probable that the carbonic acid excretion is retarded by drying, and 

 that by this means irritability may be increased. 



It is not simply loss of water, but loss beyond certain limits that 

 interferes with the life of animals. Thus loss is not an unmixed evil, 

 because, in addition to removing excretions, evaporation is an impor- 

 tant factor in the control of temperature within the bodies of animals. 

 Loss of water also tends to concentrate the body fluids, and when this 

 loss brings about a relatively dry condition, such tissues are in a con- 

 dition which is favorable for the endurance of relatively extreme low 

 or high temperature (Davenport, '97:256-258), and even dryness 

 (see references, Adams, '13 : 98-99). This is a reason why it is dif- 

 ficult to distinguish, in nature, between the effects of aridity and tem- 

 perature extremes, and hence arise the puzzling interpretations of con- 



