4 E. F. Adolph 



funnel and a tube held beneath it. Drink is taken from the 

 beaker, which can be freed from the frame and weighed at 

 intervals. The weight of the body, ascertained while the rat 

 is in the frame, measures any net change of body water 

 content, including evaporative losses. 



When an adult rat has been forcibly given an excess of body 

 water, it promptly excretes water more rapidly than usual. 

 The urine flow varies linearly with the water excess present 

 in the body, as is shown when one plots the first hour's output 



? -10 



-4 -2 +2 +4 +6 



WATER LOAD, PERCENT OF BODY WEIGHT 



•10 



Fig. 2. Equilibration diagram for water exchanges of adult 



rat. Constructed from data of Adolph (1956) and Adolph, 



Barker and Hoy (1954). 



of urine after water is forced into the stomach in relation to 

 the amount of water excess or load (Fig. 2). When the rat 

 has been dehydrated by being deprived of water for various 

 periods of time, water is drunk as soon as allowed, and the 

 amount drunk is roughly proportional to the water deficit or 

 negative load. Excretion and ingestion are symmetrical 

 activities that specifically and appropriately compensate for 

 the disturbances of water content (Adolph, 1943). Many 

 tests seem to show that the accuracies of compensation by 

 drinking and by excreting are about equal when the water 

 loads are of equal magnitudes. 



