386 PHYSIOLOGICAL EEGULATIONS 



is no evidence that exchanges in the stationary state are any more 

 or less characteristic of the organism's physiological constitution 

 than the exchanges in any other states. But they have the great 

 advantage, in common with exchanges in State I, of being indepen- 

 dent of chronology or nearly so. 



For many a component it has been observed that the more of it 

 the body has, the more of it is steadily exchanged. Or, within 

 limits R is positively correlated with C. Independently investiga- 

 tors rediscovered this for total substance, total energy, nitrogen, 

 water, and carbon dioxide. Surprise would have been saved in 

 (n-l) instances had there been any inductions concerning equili- 

 brations in steady states. 



The rich organism is sometimes (a) one that has much, some- 

 times (b) one that has credit, and sometimes (c) one that spends 

 much, either by high turnover or by temporarily reducing its con- 

 tent. All these meanings are disentangled by relating SC/At with 

 AC and C. 



The loadings and unloadings of diverse components that have 

 been studied in one species have not all been measured in the same 

 individual, nor simultaneously, nor under like conditions. Hence 

 it is by no means certain that they are comparable. Comparability 

 becomes most certain by simultaneous measurements in the same 

 individual (chapter XVII) of diverse components and of their 

 exchanges. Then the question arises whether component Ji be- 

 haves the same when J2 is also modified, and when agent Y2 is 

 substituted for Yi. 



So a study of loading and recovery consists in mensuration of a 

 group of concurrent changes. The changes found characterize the 

 agent inducing the load, and the organism reacting. The distinc- 

 tions among agents and among modified properties replace the 

 customary generalizations from isolated observations made, with- 

 out benefit of clocks, upon diverse species and under random 

 conditions. 



§ 139. Comparison of kinetic parameters 



It is desirable at this point to compare several terms that are 

 currently employed in designating the exchanges of components by 

 organisms and their parts. Names used for these quantities are 

 metabolic rate, clearance, accumulation rate, invasion coefficient, 

 permeability coefficient, velocity quotient. All are kinetic quan- 



