236 PHYSIOLOGICAL EEGULATIONS 



concentration (tig. 122) ; it even loses more than its proportional 

 share of the water that is missing from the body as a whole. Still 

 it cannot be said that ''dehydration is limited to loss of water from 

 the interstitial and from the vascular compartments. ' ' In none of 

 the actual measurements available, is it clear that plasma volume 

 or concentration is kept more nearly uniform than any other vol- 

 ume or concentration, nor is the evidence clear that cellular sub- 

 stance is protected from sharing in water deficit. 



As the dehydrations and hydrations that are observed most 

 often experimentally, happen to consist in removing or adding 

 extracellular fluid and solutes to the body, investigators have 

 gained the impression that extracellular fluids are more variable 

 than intracellular. When it is inferred that ' ' in dehydration extra- 

 cellular water is depleted before intracellular water," it is not 

 realized that the more frequent choice of conditions of sodium 

 imbalance has led physiologists to extend the prediction that the 

 whole syndrome will occur even in types of water load where 

 sodium is not much disturbed, such as desiccation by water pri- 

 vation. 



(2) Many theories suppose that water content depends upon 

 the dictates of particular nerve cells or endocrine glands. None of 

 the quantitative data that can be correlated in the present study 

 lend more support to such a view than to any other view. Possibly 

 relations of this sort are not expected to be made quantitative. It 

 appears just as likely that any (or all) of the correlations that have 

 been worked out represent crucial means of regulating the body's 

 water content. But there is here no known way of detecting a 

 crucial correlative as contrasted from an indifferent one. Perhaps 

 a physiologist not favoring such theories may nevertheless be 

 grateful to them for having suggested the gathering of data now 

 utilized in descriptions. 



§ 86. SUMMAEY 



Each of several kinds of physiological modifications is corre- 

 lated with ± AW. Further, within the conditions prevailing, these 

 various kinds are correlated with one another. Accordingly, any 

 or all of the above data might be added to an alignment chart of 

 bodily changes, or to a table of characterizations of dogs having 

 diverse loads. Further kinds of physiological activities might be 

 brought into the system of those already correlated, when adequate 



