284 PHYSIOLOGICAL REGULATIONS 



Then, so far as the one kinetic variable (water exchange) is con- 

 cerned, all those increments and conditions look quantitatively 

 alike. It may seem fantastic to homologize all the conditions under 

 which a diuresis of a certain magnitude occurs, or all those under 

 which a 3 per cent increase in dilution of plasma exists ; yet just 

 this sort of common response is a basis for analyzing physiological 

 phenomena, I think. 



(9) Other correlatives (N) such as size, forces, age, sex, per- 

 meability, of the living unit each show quantitative relationships 

 capable of extensive study. Most large species are terrestrial, but 

 it is possible to select equally sized organisms in fresh water, in sea 

 water, and on land ; both their turnover rates for water and their 

 maximal rates of water exchange are then found to be but weakly 

 related to type of environment. For the most part, rates of water 

 exchanges are in proportion to powers of body weight varying from 

 W' to B^°. 



<^ 103. Interrelations op the variables 



If variables are chosen so that not more than one of them need 

 be treated as independent, the interrelations among many may be 

 represented in a single diagram (fig. 131). In similar diagrams 

 the quantitative differences among species and tissues may turn 

 out to be almost infinite; these differences serve to characterize 

 each living unit. Uniformities are equally evident ; it is easier to 

 state these uniformities as contours in diagrams than to put them 

 in words. A nomenclature might then be invented by which to 

 designate the shapes of the contours, similar to that used for classi- 

 fying finger-prints. When the pattern of interrelations shall be 

 known for a number of species, comparison of quantities and classi- 

 fication of qualitative combinations after the manner of § 72 can 

 be carried out. But whereas there only three variables (load, gain, 

 loss) entered into 25 qualitatively different combinations, here 

 seventeen variables may yield thousands of relative types. 



So long as investigation consisted in measuring the simultane- 

 ous changes of any two factors, an enormous number of studies 

 (2""^) would be made, since the number {n) oi quantities and condi- 

 tions seems semi-infinite. Even in 2'""^' papers the interrelations 

 in water exchanges would scarcely have been touched, for the num- 

 ber of combinations of three variables at a time turns out to be 

 about 3'""^', etc. Temporarily, investigators gain satisfaction from 

 finding qualitative answers, from making two measurements at a 



