"WATER BALANCES AND EXCHANGES 287 



these the rate of water exchange was most frequently ascertained ; it 

 seemed to be specially related (by virtue of dimensions and common 

 component) to water increment and content. Sometimes the rate 

 of exchange was known only as net flow; at other times both gain 

 and loss were simultaneously measured, and either in total or in 

 paths. The symmetry of gain as contrasted with loss was stressed. 



Water content was readily disturbed under controlled and mea- 

 surable conditions by two general procedures : (a) stopping the con- 

 tinual gain or the continual loss, (b) imposing extra gain or loss. 

 Each load was initiated either gradually or suddenly, and then either 

 released from further interference or partially continued, and often 

 in such a manner that an approximately stationary state of water 

 increment prevailed. Accordingly, the several rates of exchange 

 might remain stationary within chosen limits of time ; otherwise the 

 temporarily modified rates of water exchange were measured. 



It turned out that net rates of water exchange were markedly 

 different at diverse water increments. Within the limits com- 

 patible with life, net gains appeared in negative increments (water 

 deficits) and net losses in positive increments. Hence the exchange 

 was always of a type that dispelled the increment, thereby accom- 

 plishing recovery, and compensating for the increment of water in 

 the animal. Net exchanges were zero solely when intake equalled 

 output, hence at water balance. At other contents high intakes 

 accompanied low outputs, and vice versa; gains and losses increased 

 together only in what were believed to be "forced" situations. 



When organisms or their parts were allowed to recover, the time 

 courses of water exchanges were followed. Sometimes the initial 

 rates of exchanges were the most rapid ones ; at other times delays 

 occurred. As the increment diminished with time, the rates of ex- 

 change were modified according to the relation of increment to rate 

 in steady states. Eventually the net rates decreased to zero, at 

 which time it could be said that recovery ceased. The return of 

 water up to this time was then comparable with the increment 

 originally present. 



Diverse types of water increment were produced by various 

 means, recognizing specified conditions under which recovery 

 occurred. In general, increments were absolute (such as are 

 usually measured by changes of weight or volume), or relative to 

 designated constituents (such as are usually measured by changes 

 of a concentration). The same increment might be absolutely 

 negative and relatively positive. 



