10 



E. F. Adolph 



rats drink more milk than water in recovering from dehydra- 

 tion. But in the same circumstance they drink more water 

 than sahne. Even newborn rats distinguish between milk and 

 other fluids; at 17 postnatal days they distinguish between 

 water and salt solutions. Such sensory discriminations are 

 necessary before rats can link their intakes to specific de- 

 ficiencies of bodily constituents. The actual tying of water 

 drinking to water deficiency does not certainly occur until 



1000 



0.01 0.1 



100 1000 



Fig. 8. Relation of log water content to 

 log body weight in rats from foetus to 

 adult. B = birth. Numbers represent 

 exponents in parabolic equation relating 

 the two quantities. Data of Hamilton and 

 Dewar (1938), from Adolph (1957). 



28 days after birth (Krecek, Kfeckova and Dlouha, 1956). 

 Already then the water intake of rats equals the water deficit 

 imposed upon them (Adolph, Barker and Hoy, 1954, fig. 13); 

 just as in the adults, the one-hour intake closely matches the 

 water deficit so long as the water deficit does not exceed six 

 per cent of the body weight. 



Once the immediate regulations of water content are fixed, 

 the adult method of maintaining water balance is persistently 

 at work. But it is well recognized that the water content, 



