VAKIABILITIES OF WATER RELATIONS 87 



slightly in excess of the believed load and proportional to it (chap- 

 ter II). 



Recoveries from numerous types of water excess and of water 

 deficit were compared, each type representing diverse states of the 

 dog and diverse conditions for recovery. Several criteria were 

 found whereby a water load might be distinguished from a new 

 water content in water balance. It was suggested that all modifi- 

 cations of water exchange and of water content may be classified 

 qualitatively, while within each class quantitative diversities pre- 

 vail. These types represent the physiological states of the dog, the 

 diverse accompaniments of the water administration, and the paths 

 by which water is administered and returned. Selection of those 

 environments in which water losses are minimized and access to 

 water is easy, may be of significance in maintaining the character- 

 istic water content (chapter III). 



Physiological variation of water content in dogs serves as a 

 measure of its regulation. With respect to short periods of time, 

 successive variation often differs from random variation, denoting 

 a temporal characteristic of possible governors. Several methods 

 of evaluating and comparing the variabilities and their sequences 

 are suggested, both for contents and for rates of exchange. Rate 

 of water gain is not more variable than rate of water loss in periods 

 of 24 hours, but in periods of 1 hour gain is much the more variable 

 of the two. No further evidence was found that content is regu- 

 lated more accurately either at gain or at output, and compensa- 

 tions for departures from balance occur equally at both. In ex- 

 changes during recoveries the variabilities are relative to the mean 

 rates rather than absolute (chapter IV). 



