292 PHYSIOLOGICAL REGULATIONS 



(21) Animals frequent environments that furnish water to 

 them, or that minimize loss of water. Both behaviors are exag- 

 gerated in water deficit. 



(22) In water increments of the whole body, plasma is diluted 

 twice as much as the whole body (dog). Whole blood dilutions are 

 less certainly correlatives of load. 



(23) Volumes of distribution of several injected distribuends 

 also change markedly more than does the whole body (fig. 114). 



(24) Most tissues analyzed share in the distribution of excesses 

 and deficits of water, at least in four species (table 29). In diverse 

 species no one tissue preserves its water content more consistently 

 than others. No outstanding depots of reserve water have been 

 identified. 



(25) Hence very many living units, whole individuals, their 

 parts and aggregates, of diverse species, may be studied with re- 

 spect to water loads ; and similar patterns are found in their main- 

 tenances and recoveries of content. 



These conclusions are arrived at from correlations which are 

 explicit here. Further tests of their generality lies in additional 

 information. At present none is known to me that contradicts any 

 one conclusion. But generalizations are always provisional; it is 

 not improbable that organisms exist which fail to fit some of the 

 specifications of those studied thus far. It does seem to me im- 

 probable that any species of organisms exists whose individuals 

 are wholly without means of adjusting their water contents ; and 

 regulation of this function may be one of the many requisites for 

 survival. 



Quantitative conclusions do not lend themselves to statement in 

 words ; they can be fully reviewed only by reexamining the diagrams 

 and tables. 



§ 107. Diversities 



Comparisons among species and among parts of organisms that 

 were modified in water loads, revealed features of difference that 

 are not known to be mere corollaries of structural difference : 



(1) In frog, earthworm and ciliate (in fresh water) the rates 

 of water gain are no less in water excesses than in turnover. 



(2) Some whole aquatic animals (Phascolosoma, Arbacia egg) 

 manifest no turnover of water ; in them recoveries of water content 

 are accomplished through exchanges of novel sorts, instead of 

 through quantitative modifications in paths already operating. 



