186 



PHYSIOLOGICAL EEGXJLATIONS 



The values of quotients depend in part upon the intervals of 

 time allowed for initial recovery, and upon the conditions within 

 and without the organisms. Each species and each part of an indi- 

 vidual in a sense competes in speed of water exchanges with each 

 other, be it under supposedly similar or different conditions. 

 When the numerical values of 1/At are examined, the dog's recov- 

 ery from deficits and the rat's recovery from excesses are found 

 to be the most rapid; the snake's recovery from excesses is the 

 slowest. There is no apparent relation of velocity quotient to the 

 anatomical elaboration of organs of water exchange, though their 

 spreads of surface are probably factors. 



Hours 



Hours 



Tig. 107. Exchange curves for water in 4 species; rate of net water exchange (% 

 of BoAour) in relation to time. Gains in deficits, solid lines; losses in excesses, broken 

 lines. Two selected average curves are represented having numerically equal initial loads. 

 Dog, from figures 2 (A) and 10 (AW -4.6); Phascolosoma, from figure 86 (AW -24 

 and +31) ; Man, from figures 50 (A) and 57 (P2) ; Frog, from data of figure 67. 



Hence it is often possible to represent the whole of a recovery 

 by one parameter, relating water load, rate of net water exchange, 

 and time. In appropriate species the one parameter in turn 

 characterizes the response to load of any magnitude at all times 

 during the recovery. Wherever concentrations either are effective 

 in moving water (as in Phascolosoma) or serve as stimuli to mov- 

 ing water (possibly in dog), rate of exchange might have been 

 expected to be proportional to load anyway. But numerous rates 

 are proportional to load also where entirely different processes are 

 inferred (as in intake of man). 



