272 



PHYSIOLOGICAL EEGULATIONS 



organism. I presume that an intensity of the sort meant is mea- 

 sured by the rate of water exchange ; and there the rule holds. Of 

 course, when exchanges are measured as fractions of the body 

 weight per unit of time, all the rates diminish with greater body 

 size ; actually, they vary as some power of weight that is less than 1. 

 Since all measures of size are correlated with others, any one of 

 them that can be accurately and conveniently measured is preferred 

 for use. Usually that one is body weight. 

 1-2 



Log Body Volume— ml. 

 Fig. 140. Eate of water exchange in relation to body volume among many species 

 of aquatic animals. Both scales are logarithms of either ml. or ml./hr. Maximal rates 

 (from table 13) are either for output in positive loads (solid triangles) or for intake 

 in negative loads (open triangles): EB,ax = 0.50 Bo.66. Turnover rates (from table 

 21) are either for marine species (solid circles) or for freshwater species (open circles) : 

 Eto = 0.016 Bo-75. 



(3) Additional features. Special structures and shapes, such 

 as the ears of the rabbit and the wings of the bat, may modify the 

 correlations of rates of water exchange with size among species, 

 as in every other relation of body size. No attempt is made here 

 to sieve out the partial correlations of water exchanges with pul- 

 monary ventilation rates, kidney weights, oxygen consumption 

 rates, and a host of other quantities. Two or three more selected 

 variables will, however, be followed. 



