Physiological Regulation of Water Content 9 



diuresis that is large and sudden even a few hours after birth. 

 Likewise, adrenahne or noradrenaUne induces a full-blown 

 diuresis on the very day of birth. Evidently the capacity for 

 excreting water at a high rate is present, but its arousal 

 depends on the particular form of stimulation. Consequently, 

 any discussion of structural inadequacies or functional im- 

 maturities seems beside the present main point, which is 

 that the specific responding system of the newborn rat is not 

 tuned to water excesses. 



Hence, we are privileged to see a physiological regulation 

 increase in intensity in the growing individual. The regulation 



10 20 



Fig. 7. Courses of development of four types of diuresis in 

 rats. B = birth. From Hoy and Adolph (1956). 



duly materializes, whether the rat has ever experienced a 

 water excess or not; the elements necessary for it are there, 

 some of them long before this materialization. What guides 

 the regulation's intensity and determines its point of adult 

 fixation is unknown. The fixation is still subject to a small 

 degree of adaptation resulting from previous exposure to 

 water excesses (Adolph, 1956). 



The control of water intake, on the other hand, is much less 

 understood than the control of water elimination. In early 

 infancy, rats, like dogs (iVdolph, 1943, p. 267), refuse to drink 

 water, even after dehydration. According to K?ecek, Kfec- 

 kova and Dlouha (1956), as late as 28 days after birth young 



