Physiological Regulation of Water Content 7 



antidiuretic hormone until the water excess is removed. This 

 theory is widely accepted for mammals generally. In infant 

 rats above five days of postnatal age we found that water 

 diuresis was inhibited by injecting pitressin (Fig. 5). But at 

 two days of postnatal age the diuresis was unabated by this 



HOURS 



Fig. 5. Water diuresis at two different 

 ages in infant rats (dash lines), and the 

 effects of pitressin injections at P upon 

 it (sohd Unes). DA = days after con- 

 ception. From Adolph (1957). 



substance. It is unlikely that the foreign pitressin is in- 

 activated at one age and not at another, and possible that 

 infant renal tissues are insensitive to it (Heller, 1952). But 

 the most important conclusion is that diuresis can be aroused 

 by some other means than the withholding of the hormone in 

 the neurohypophysis. At this particular age of two days a 



