132 



PHYSIOLOGICAL REGULATIONS 



in other species, urinary loss is the path that adjusts itself so as to 

 compensate diverse positive loads. In the rat diuresis begins and 

 becomes maximal slightly sooner than in dog, man, or rabbit. In- 

 gestion, on the contrary, is slower than in most. When allowed 

 alternative environments, rats choose moist atmospheres, and 

 choose them more frequently in extreme deficits of water. All 

 these kinds of regulations are restorative and preservative of water 

 content. 



§ 44. Garter snake. Reptiles 



Perhaps the general processes of water equilibration have now 

 been explored in mammals. What do reptiles do to preserve and 



30- 



U 20- 



10- 



-30 



'ZO 



-10 







+10 



+20 



Water Load 

 Fig. 80. Initial rate of net water exchange (% of BoAour) in relation to total 

 water load (% of Bo). Equilibration diagram, garter snake, Thamnophis sirtalis. 

 First 1.0 hour. Seven individuals of 6 to 103 grams body weight (without food) have 

 been desiccated for 2 to 12 days at 23 to 28° C, or injected intraperitoneally with dis- 

 tilled water. F, line representing the data, and the theory that E^ = -AW. G, line 

 fitted by inspection, Ew = + 0.14 AW. New data. 



reestablish water balances'? The snake, Thamnophis sirtalis, was 

 subjected to diverse water contents, deficits being established by 

 confinement for several days without water, and excesses by sudden 

 intraperitoneal injection of glass-distilled water. 



Total water loss from a snake in a closed jar at 25° to 30° C. is 

 of the order of 0.02% of Bo/hour, and does not increase appreciably 

 at molting of the skin. In a wire cage it is greater by 5 fold, indi- 

 cating the prominent role of evaporation. It is not known where 

 the evaporation is most rapid (lungs, mouth, skin, mucosae). 



When allowed water the desiccated snake puts the mouth into the 

 liquid and moves the walls of the mouth rapidly. With considerable 

 accuracy it drinks, usually within 0.1 hour, nearly the amount of 



