288 PHYSIOLOGICAL REGULATIONS 



Behavior toward water in environments was of two sorts : cer- 

 tain animals were able to locate water, usually without seeing it; 

 and certain animals frequented moist air instead of dry. In both 

 sorts, the preference for water or moist air was exaggerated when 

 the body was in water deficit. Statistically significant preferences 

 for environments that tend to diminish water losses and favor water 

 gain thus play a role in the maintenance of water content. Not all 

 species are known to show evidence of preference for water in 

 environment ; some may accept whatever comes, just as tissues and 

 some parasites in situ do. 



Variabilities of water content and of water exchanges measured 

 the net results of regulation. One individual undergoes continual 

 fluctuation of each, but the narrow or wide limits within which it 

 varies indicated how sensitive the system of organism plus environ- 

 ment is toward increments of water. Frequencies of reversals, 

 precisions of rates, and durations of movements, served to char- 

 acterize the processes of maintenance. 



So long as the study of water was confined to the factors of 

 increment and time, variables of four classes of dimensions were 

 dealt with: content (AW), exchange (SW/At), time (t), and velocity 

 quotient (1/At). For each species and set of conditions, certain 

 numerical characterizations among these four were selected, which 

 by their uniform relations allowed many comparisons. These were : 



Rates; turnover, initial, stationary, minimal, and maximal 

 (tableslO, 13, 15, 21). 



Economy quotients (table 9). 



Modification ratios (table 11). 



Augmentation ratios (table 11). 



Tolerance curves (fig. 106). 



Tolerated loads (table 22). 



Variabilities; successive, individual, within species (table 12). 



Acceleration and decelerations of exchanges (table 14). 



Periods ; latent, recovery, to maximal rates (table 14). 



Half -life (any fractional-life) of load (§ 7, table 32). 



Precisions of turnover (§23). 



Completenesses of recovery or return (§7). 



Partitions of exchange (tables 10, 11, 20, 17). 



Equilibration diagrams (fig. 110). 



Usefulness of comparisons made according to these criteria is 

 illustrated in the various tables. In general the comparisons drawn 



