2 PHYSIOLOGICAL EEGULATIONS 



it would be quite arbitrary to consider traditionally functional 

 aspects of organisms by themselves, and the term physiological 

 merely indicates the aspect to be stressed here above others. 



And now the questions are : how may this recognition of con- 

 stancy be removed from the limbo of vagueness, and subjected to 

 quantitative study? What shall be measured to assure me of the 

 concrete existence of regulations 1 How may a physiologist record 

 what an organism is doing to maintain its functions so constant? 



Why does anyone investigate constancies anyway? Various 

 excuses have been set forth by others for this perennial interest. 

 Any property seems worth knowing about, just in proportion to 

 its prevalence. Constancy of function is a feature of whatever 

 constituents and manifestations have been observed in all organ- 

 isms. By the degree of constancy I can characterize diverse mani- 

 festations in one species, can compare similar manifestations in 

 diverse species, can ascertain what each animal does to insure con- 

 tinuance of function, and can observe how the animal manages 

 many properties simultaneously. If I had not guessed at ways to 

 investigate how constant various components are, and what hap- 

 pens when a component is disturbed, I might have been content 

 with lip service to the existence of constancies. But now that some 

 of my guesses have found substantiation in data and correlations, 

 I am not satisfied with anything less than a quantitative treatment 

 of the elements concerned. There is nothing in physiology or any 

 other science to indicate that understanding is promoted by not 

 intimately prying into the relations involved in a class of phe- 

 nomena. 



I propose first to outline briefly the subject of maintenance of 

 physiological constancies, giving the methods, results, and conclu- 

 sions that I have found appropriate. Thereafter, a more detailed 

 and ordered treatment of the material will be given, leading to 

 each of the generalizations to be mentioned. Since my generaliza- 

 tions have arisen in the study of water relations of animals, it is 

 most direct to use water content as the property whose constancy 

 shall be visualized (Part A). Whatever further features can be 

 found with respect to content or manifestations of other com- 

 ponents of organisms can be noted later (Part B). 



In an early stage of physiological science the statement was 

 often made that an organism's water content is kept constant by 

 virtue of kidneys, or integuments, or some other structures. Later 



