UNIFORMITIES AND COMPAEISONS AMONG COMPONENTS 371 



may be computed, or vice versa; for, the difference between total 

 gain and net exchange is the total loss. 



It may be induced from equilibration diagrams that at two 

 diverse loads, the same rate of exchange would not be expected to 

 occur. Yet it is sometimes assumed that a measurement of rate 

 of net loss, for instance of nitrogen during nitrogen deficit, is a 

 measurement of turnover in balance. 



Wherever positive loads have been investigated, negative loads 

 may be expected to be of equal interest. The history of physiology 

 shows, however, that intensive studies of changes in one have not 

 often led to inquiries into the paired state. This omission indi- 

 cates that other considerations than quantitative symmetry of 

 function have guided investigations. 



The range of loads observed in the study of each component is 

 limited. Occasionally little experimental effort is put into obtain- 

 ing extreme states (tolerated loads), while in some instances the 

 production of injury (irreversible change) in the organism is ap- 

 proached. The criterion of irreversibility is open to many differ- 

 ences of judgment or end-point; perhaps the criterion of ''death" 

 (judged by a chosen independent test) within a certain number of 

 hours from the time at which the load is imposed, is a generally 

 useful measure of tolerated load. Each component may then be 

 varied within the range stretching from mean viability in negative 

 load to mean viability in positive load. 



The magnitude of load in the stationary state or at the maxi- 

 mum is as much a function of the rate of recovery as of the agent 

 impinging. For, the maximal load is a sum of gain and of loss, 

 and since rate of loss usually emulates rate of gain, it is often the 

 case that no acceleration of gaining will long outdistance losing. 

 An analogy is throwing a ball vertically; acceleration of gravity 

 becomes equal to acceleration of lift at a very finite height. 



Overshooting of the content characteristic of balance, did not 

 regularly occur during recovery in any of the components here 

 reported (cf. Burton, '39). In quantitative comparisons of diverse 

 components a problem is to find commensurate coordinates, for^ 

 both loads and rates are measured in a variety of units (table 40), 

 For certain specific comparisons, common units are available; 

 calories, grams, chemical equivalents, weights, volumes ; these rep- 

 resent appropriate particular equivalences of energy or of sub- 

 stance. For other purposes it is preferable to record every load 



