8 E. F. Adolph 



response is thus uncovered which is mediated through some 

 other channel ordinarily masked by the known hormonal one. 

 The intensity of diuresis is a function of the water excess 

 at all ages (Fig. 6), but the regression differs with age. Actually 

 these data supply part of an equilibration diagram for infant 

 rats, and by it one can watch the regulatory relations coming 

 to maturity during early postnatal life. The unexcreted water 

 has been located as excess in plasma and several other tissues. 

 A possible theory of maturation is that some slowly develop- 

 ing process or structure limits the rate of water excretion. 



WATER LOAD. 7o OF WT. 



Fig. 6. Water exchange in urine in relation to body water 

 load at each of three different ages. DA = days after con- 

 ception. From Adolph (1957). 



This theory is doubtful, since at every age still greater water 

 excess arouses faster excretion. Rather, the response, ex- 

 pressed by the ratio between excretory rate and water load, 

 is small at birth and becomes greater as age increases. 



However, in order to see whether diuresis is impossible at 

 birth, we tested the capacity of the infant rat to respond to 

 several other stimuli of diuresis. To concentrated salt solu- 

 tions the diuretic response is practically nil at birth, and it 

 matures even later than the water diuresis (Fig. 7). Hypoxia 

 arouses a primary diuresis that is small at birth and becomes 

 greater a few days later ; it also, however, arouses a secondary 



