WATER RELATIONS OF OTHER SPECIES 



127 



other diversities of the species is discernible. Drinking is, further, 

 a specific process; for a concentrated solution (M/1) of sodium 

 chloride is consistently refused. But a dilute solution (M/4) is 

 ingested, though in lesser amounts than water ; and when its con- 

 centration is compared with the "optimal" concentrations of uri- 

 nary output and of solute intake found by Gamble et al. ( '29, '34), 

 it may be inferred that considerable net water is gained or made 

 available after the latter solution has been metabolized. 



0.4 0.8 1.0 



Hour 

 Fig. 76. Course of sensible water load (% of Bo) during recovery from water 

 deficits in rat. In each test a rat has been deprived of water but allowed food for 24 

 hours before zero time. Then water or NaCl solution (M/4, M/2, or M/1) is made 

 accessible in a burette. Bars indicate standard errors of amounts of water ingested 

 at diverse times. New data. S shows the mean ingestion of water in 6 tests of Skinner 

 ('36), the initial and final points being made identical with those of curve W. 



The shape of the tolerance curve in recovery from water deficit 

 is independently confirmed by tests of Skinner ('36, '38) which in- 

 volved a behavior more highly conditioned than drawing water 

 from the open bottom of a burette (S, fig. 76), namely, pressing a 

 lever to obtain each aliquot of water drunk. Apparently the ma- 

 chinery utilized did not delay the rat in getting its water. In an- 

 other less detailed study with the "obstruction" method by Warden 



