WATEE EXCHANGES OF DOG 23 



Water is gained during these periods of water excess in only 

 small amounts. When water is offered, the dog consistently re- 

 fuses to drink it. Small quantities are being continually formed 

 in the body by oxidation of organic compounds containing hydro- 

 gen, and possibly by other processes, which do not vary signifi- 

 cantly with water content or load (Bidder and Schmidt, 1852; 

 Rubner, '02, p. 62; Heilner, '07; Lusk, '12). 



In general, losses of water are enormously increased, while 

 gains of water are somewhat decreased, for some hours after water 

 is given by stomach. The greatest modification is in rate of uri- 

 nary output. 



The full amount of water ingested is only rarely realized or 

 returned in the urine before the rate of urine formation comes back 

 to approximately that of the control state. After administration 

 of more than 2 per cent of the body weight, about 76 per cent is 

 returned as urine in 3 hours (fig. 3). In total output the corre- 

 sponding return is 82 per cent of the volume ingested (fig. 1). If 

 corrections are made for the basal (control) rates of water loss, 

 either urinary or total, the return is still less. Apparently the body 

 does not treat quite all the water administered as excess. Some- 

 what greater returns than those exhibited occur only after special 

 preparation for the experiment, consisting in a previous adminis- 

 tration of an excess of water on the same day (Klisiecki et al., '33a ; 

 Kingsley and Adolph). 



Not only can the returns be ascertained after diverse periods of 

 time have elapsed, but from figures 1 to 5 may be read the times 

 required for initiation of diuresis, for maximal rates of excretion, 

 for half return or half -life (or any other fraction) of the adminis- 

 tered load, and for cessation of diuresis. All of these intervals of 

 time except that for initiation are longer as the load is greater. 



Figures 1, 3 and 5 represent loads in relation to time. This 

 relation in certain components of organisms is commonly termed a 

 tolerance curve; the designation may be applied therefore to all 

 curves relating load to time. I suppose the "logic" of the word 

 tolerance is that the curve indicates how much added component 

 the organism tolerates by removing it. High tolerance for water 

 means fast disposal of an excess or a deficit of it, the opposite of 

 indifference toward the increment. Rates of exchange in relation 

 to time (figs. 2 and 4) may be designated as exchange curves. 



Water content in control conditions is approximately propor- 



