296 physiological regulations 



§ 109. General theories op water constancy 



A number of theories have been proposed concerning water in 

 animals, as they have concerning every other aspect of organisms 

 that has been observed, aiming to picture in one way or another the 

 maintenance of constant water contents, (a) One theory states 

 that forces related to protein constituents of tissues hold water 

 there. ''Absorption of water by muscle is determined in the main 

 by the state of the colloids contained in the muscle" (Fischer, '10, 

 p. 74). (b) Another suggests that the water content of tissues is 

 governed by the ratio of cholesterol to phospholipid in them (Mayer 

 and Schaeffer, '14). (c) Again, hydrostatic pressures and partial 

 osmotic pressures may be balanced when water is distributed 

 equitably between a unit of tissue and its surroundings (Starling, 

 1896; Schade, '27). (d) Or, perhaps the total quantities of solute 

 present in the whole body dictate the quantity of water held (Gam- 

 ble, '29). 



Emphasizing water exchanges, (e) Rowntree ('22) said, "The 

 total output of water is determined by the total intake," and 

 further, ' ' The need of the body for water is determined largely by 

 environment and metabolism." (f ) Reversing the terms, Richter 

 ('38) stated, "Maximum intake may be determined by the maxi- 

 mum capacity of the kidneys," while "it would seem likely that the 

 maximum output is determined by the total fluid capacity of all the 

 cellular spaces of the body." (g) Very often it is supposed that 

 the kidneys watch over the water content of the body, while nothing 

 is said concerning organisms that have no kidneys. These last two 

 hypotheses seem to have been framed to apply to certain mammals. 

 Explicitly limited is (h) the inference of Babcock ('12) that "the 

 water requirement of mature animals that excrete urea, when at 

 rest, depends chiefly upon the amount of digestible protein con- 

 sumed." (i) Adolph ('33) thought the requirement of mammals 

 might be predicted by adding together the factors of nitrogen, salt, 

 and energy metabolisms. These last two ignore the general ex- 

 perience that some other investigator will experimentally raise 

 another factor to first magnitude, requiring another statement to 

 express the relationship. 



In general, all these and many other views may partially cor- 

 respond to facts, but not in the manner hypothesized, for all are 

 aspects of a large picture that I believe is one of numerous interrela- 

 tions. There is much evidence that no factor D is invariably cor- 

 related with water content W, and much that many factors E, F, G, 



