Chapter VII 



WATER RELATIONS OF OTHER SPECIES 



§ 41. The present account of regulations of water content might 

 be limited to man, or to mammals, or to vertebrates. Such limita- 

 tion would leave out myriads of other classes of animals ; I judge 

 that more insight is to be gained by extending considerations to 

 many kinds. Are regulatory processes present wherever they are 

 sought? Do animals forestall the need for compensations of dis- 

 turbed water content, by frequenting appropriate environments? 

 Do some species depend on adjustments of output to do the same 

 thing that other species accomplish by adjustments of intake ? Are 

 special structures concerned in compensatory exchanges wherever 

 such adjustments are found? 



Two kinds of interest (at least) might attach to data concerning 

 water regulations in varied parts of the animal kingdom. General 

 physiology might have its dream come true of knowing exactly how 

 general each of the processes and correlations concerned in water 

 exchanges actually is. Comparative physiology might fairly rate 

 various phyla and species according to their means of disposing 

 of water loads and the kinetics of their exchanges. The perfect 

 dream might require data upon a thousand species. I believe that 

 a fair outline of the features of all water regulations is obtainable 

 from the fifteen or twenty species for which appropriate though 

 partial data exist. 



My plan is to present briefly the pertinent information concern- 

 ing water exchanges in each of those several species. Special 

 methods are required for the study of each, and particular features 

 are to be noted. Thereafter (chapter IX) , quantitative similarities 

 and diversities will be ascertained. Comparisons are not limited 

 to animals possessing any one common structure except ''proto- 

 plasm"; wherever exchanges of water occur they either do or do 

 not serve regulations, and in diverse degrees and patterns. 



From knowledge of water relations in dog, man, and frog, the 

 following physiological arrangements might, as a first extrapola- 

 tion, be expected in other animals : (a) a water content varying less 

 than ± 3% of Bo at intervals of 24 hours, (b) a turnover, (c) a 

 compensatory recovery by augmented rates of loss when excesses 



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