396 PHYSIOLOGICAL EEGULATIONS 



that may have discouraged the previous realization of quantitative 

 equilibrations: (1) Until recently, long periods of time were used 

 in measuring metabolisms and other rates of activity. Hence re- 

 covery of balance was often completed before the measurement of 

 exchange was made. (2) Conditions of balance were preferred; 

 turnover and minima were ascertained first. (5) Loads were mea- 

 sured chiefly in blood. But the rates of exchanges by blood were too 

 rapid to measure in some instances ; it was difficult to assmne that 

 volume of blood was constant ; and only net rates of change in con- 

 centration were ascertainable. (4) It was supposed that all the 

 separable processes of exchange needed to be labelled before de- 

 scription of the exchanges could be undertaken. For the most part, 

 however, the materials were at hand, and a mere shift of inquiry 

 finds new relations present among them. 



The specification of conditions for study, of course, suggests 

 innumerable further studies by these procedures. Equilibrations 

 would be concerned with all the capacities of living units to combat 

 excesses and to make up deficiencies. In a general way several bio- 

 logical sciences are mainly concerned with just these ; particularly 

 toxicology, pathology, ecology, and physiology. One of the imputed 

 virtues of a scheme like that of the equilibration diagram might be 

 that one investigator need no longer be a specialist on one com- 

 ponent. Rather, having studied the relations of Ji in one living 

 unit Ui, he is now qualified to tackle any J in any U with which he 

 is interested in becoming familiar. He may revel in any quantita- 

 tive relations and not be confined to a single component. 



What quantities (components) in organisms are susceptible of 

 study by equilibration diagrams ? I should predict that any mea- 

 surable characteristic of any living unit may be correlated with the 

 rate at which the same characteristic changes. Seemingly any pro- 

 cedure for quantitative measurement, any organism, and any clock, 

 are all that are requisite to the investigation of an equilibration. 

 The devices or procedures employed are not limited to those 

 familiar in any one field of biology or of non-biological science. 

 Wherever there is a definable system, changes occur in it whenever 

 displacements or increments of component occur. 



§ 143. Summary of the variables studied 



For any one component, some nine sorts of quantities were 

 investigated. These were roughly classified (§ 101) into three dis- 



