WATER RELATIONS OF MAN" 103 



loss that increase with water excess ; at its right a limb shows maxi- 

 mal rates changing little with load, (o) the rates of ingestion are 

 approximately proportional to water deficits, and zero in water 

 excesses, (p) The rates of loss and of gain are equal at one point 

 of balance, (q) In excesses, loss exceeds gain; in deficits, gain 

 exceeds loss; so that in both balance is regained, (r) Losses are 

 slightly decreased in water shortage, both by urinary and by evap- 

 orative paths, (s) Oxidative gain is approximately uninfluenced 

 by water load. 



Both uniformities and diversities between two species of mam- 

 mals having been found, it is worth while to inquire which uni- 

 formities hold for others as well. The pattern of the equilibration 

 diagram for dog and man may be found in many other species, but 

 its quantitative features show wide diversities of magnitudes. 



<§. 32. Variations 



A more intimate notion of the exactitude of water balance of 

 man is obtained by the study of fluctuations in content and in ex- 

 changes. Near water balance intake is much more variable than 

 output over periods of 0.25 hour (table 12), although one path of 

 it (oxidative gain) is very constant under standard conditions. 

 Often water content (body weight) slowly decreases from quarter- 

 hour to quarter-hour until water is taken to restore it in part. No 

 great differences from the dog in this respect (§22) have turned 

 up. 



Stability of a physiological function is sometimes said to be a 

 partial measure of, as well as a usual requisite for, the organism's 

 success (in surviving). The criterion of success, however, may 

 equally be otherwise and diversely chosen (leading to confusion of 

 terms unless specially defined), since the small fluctuations of 

 water content now discussed are not known to affect survival. 

 Some kinds of ' ' success ' ' are dependent upon greater rather than 

 less variability. In the social organism, too, great stability is not 

 always beneficial to survival (Pareto, '35, § 2195). 



In addition to random variability, it is necessary to distinguish 

 oscillations or rhythms of function, either with respect to time or 

 to some other variable. In the case of water exchanges these 

 periodic fluctuations have been measured in man under continued 

 water drinking. In the average individual, urinary outputs (dur- 

 ing uniform hourly intakes) are said to vary in four cycles per day 



