] 05 ^^^ mouse that never drinks 



can, it has been demonstrated, get along without drinking 

 at all. But he also must have succulent food. Dipo, on the 

 other hand, belongs in an entirely different class. It is not 

 only that he can get along without water. He will not take 

 it if it is offered to him. And he does not have to have any 

 succulent food either. He can live indefinitely on the driest 

 of dry seeds. 



This fact has been abundantly demonstrated by brutally 

 thorough and rigorously controlled experiments. Kept un- 

 der desert conditions of heat and of dryness for fifty-two 

 days and fed on an exclusive diet of dried barley seeds, 

 Dipodomys merriami not only lived but, when subjected 

 to a post-mortem examination, showed no diminution in 

 the proportion of water to total body weight; and that re- 

 mained true even of those of the victims who gained in 

 total weight during the course of the experiment. "Control" 

 individuals who were given access to watermelon during 

 the same period and w^ho ate some of it retained no more 

 water in their blood or tissues than did those who had 

 eaten only dry food. As a matter of fact, Dipodomys needs 

 to maintain the same water content in his blood as other 

 rodents and will die from dehydration at about the same 

 degree of deficiency in this respect. 



The secret, then, is not merely the one we have met so 

 often — rigid economy in the expenditure of water. In the 

 first place, you cannot save what you have not been able 

 to get. In the second place, Dipodomys isn't even as stingy 

 in this respect as some other creatures. Unhke some insects 

 and all birds, he does not save water by voiding uric acid 

 only in solid form, though his urine is about twice as con- 

 centrated as that of the white rat, and when fed on dry 

 food his excrement is forty-five percent water as compared 



