Physiological Regulation of Water Content 5 



The relations of exchange to content shown in Fig. 2, the 

 equiUbration diagram, form a useful basis for understanding 

 the regulation of body water, and of many other body con- 

 tents. They show the specificity of the responses required 

 for constancy, the sensitivities with which they occur, their 

 promptness and their accuracy. A fixed set of relations, 

 therefore, automatically keeps the rat in water balance. 

 Similar relations have been worked out for a number of 

 other species among mammals, other vertebrates, and some 



Bladder. 



B/adder Wall ■ 



VisceraC Peritoneum 



Parietal PerUoneum 



Red us Muscle 



Fa I 



SAin 



Flanc 



~V\lire 



Fig. 3. Bladder cannula and its method of placement in 

 infant rat. From Hoy and Adolph (1956). 



invertebrates (Adolph, 1943). Much effort has also been 

 expended by investigators to find through what messages and 

 effectors the adult's automatic responses are excited and 

 mediated; those features will be largely neglected here. 



Are these relations also present in young animals, and when? 

 Are they the same as in adults? This question we tried to 

 answer particularly for water excretion, and first for newborn 

 dogs (Adolph, 1943, p. 267). For rats we needed an accurate 

 method for measuring urine flow at all ages, and eventually 

 found it through placement of a plastic cannula in the bladder 

 (Fig. 3). Urine is thereafter collected by exserting a capillary 

 glass tube on the cannula, and measuring the position of the 



