174 PHYSIOLOGICAL EEGULATIONS 



variation, with respect to (a) total intake or total output, and (b) 

 diverse paths of intake or of output. Rate of total intake is more 

 variable, in successive 1-hour periods, than rate of output in dog 

 and man, and probably in mammals generally. Variation of intake 

 is about equal to variation of output in frog and perhaps in aquatic 

 organisms generally. In the environments and conditions chosen 

 for study there is also an inverse relation, it seems, between the 

 variability of rate and the steepness of the correlation line in net 

 equilibration diagrams (fig. 47). This steepness is also expressed 

 in net velocity quotients of diverse species. 



Among species and environments there is a direct correlation 

 between rate of turnover and variability of content (table 12). Or, 

 the more water passes through the body, the more chance there is 

 for net retention or expulsion of some of it (§ 38). 



Among mammals it is evident that large body size goes with less 

 variation of content (in % of Bo), and less turnover (in % of Bo). 



(4) Maximal rates of exchanges, found at extreme water loads 

 in each of the organisms studies, may not be regarded as absolute 

 values for the species. Provisionally maximal rates of urinary 

 output, evaporative loss, and ingestive gain are recorded in table 

 10. Table 13 compares the maximal rates observed in whatever 

 species the states of water excess or water deficit were tested. 

 Many possible dimensions of the body might be correlated with 

 these rates ; the hope of finding a limiting factor in the structure 

 or use of the alimentary tract or the urinary apparatus or any 

 other one provision cannot be seriously entertained, for single 

 ''bottle necks" do not often characterize physiological processes. 



(5) Ratio of rates occurring simultaneously in any two paths 

 may represent the partition of flow (table 10) during turnover in 

 balance as well as in recoveries. For example, wishing to charac- 

 terize adrenalectomized dogs, Uyldert ( '38) showed that the ratio : 

 urinary loss/ingestive gain, which was in normal dogs 0.46, was 

 unchanged by unilateral adrenalectomy, but was increased to 0.64 

 by either bilateral excision of adrenals or by adding sodium chlo- 

 ride to the diet. 



Thus, each specific purpose suggests a feasible method of com- 

 paring rates of exchange. If one of them does not emphasize the 

 unusual features in an experimental test or in a species, another 

 will. Altogether it is unlikely that all methods will yield signifi- 

 cantly identical results for two species or metabolic states. 



