276 PHYSIOLOGICAL, KEGULATIONS 



tion of these may be deferred to a later chapter (XIV). In '^ cold- 

 blooded" animals, rates of water exchanges may be studied over 

 ranges of as much as 35° C. With respect to turnover, data on 

 frogs show "temperature coefficients" for ten degrees C. up to 2.6 

 (Krause, '28). Whether maximal rates of intake or of output in 

 water loads increase proportionally would be interesting to know. 



Season makes a difference in turnover rates at equal tempera- 

 tures, according to DeHaan and Bakker ('24), winter frogs show- 

 ing half the rates of summer frogs. This may involve many differ- 

 ences of metabolism that have not yet been correlated. It may be 

 remarked that analyzable water contents of frogs also vary with 

 temperature and with season (Donaldson and Schoemaker, '00; 

 Gaule, '01), corresponding to upward shifts of equilibrated body 

 weight (Bo) at temperatures below 9° C. (Adolph, '27a; Rey, '38, 

 p. 1113). 



Rates of water exchange were compared at five temperatures 

 in Arbacia eggs (Lucke et al., '31). For swelling in 60 per cent sea 

 water, the rate of entrance of water and the permeability coefficient 

 increased 2.7 fold for ten degrees C. rise in temperature. For 

 shrinking (recovery) the same factor was 2.4. This means that 

 the equilibration diagram (fig. 91) increases its ordinates in that 

 proportion. 



If close comparisons of water relations among species are to be 

 made, a single body temperature might be chosen for many species, 

 but no one temperature would be suitable for all. Warm-blooded 

 animals automatically fix the temperature of the body ; cold-blooded 

 animals are subject to conditions imposed by the investigator 

 within limits. Whatever temperature is imposed is inevitably open 

 to objection on some other grounds. Hence it may be explicitly 

 stated that most of the quantitative comparisons of water ex- 

 changes would be different at other temperatures from the ones 

 represented, and that a particular relation between exchanges and 

 temperature characterizes each species. 



§98. Races 



Do racial differences also matter? Closely related species or 

 subspecies of animals frequent diverse environments, foods, and 

 climates. Attempts have been made to relate whatever racial 

 diversities prevail to the rates of water intakes in deer-mice. Com- 

 parisons may here be limited to simultaneous tests under identical 



