442 PHYSIOLOGICAL REGULATIONS 



The parts played in recovery by the gains and the losses appear 

 to me to represent one common denominator in the interests of all 

 physiologists. 



(3) Paths of exchange may be classified. Such categories as 

 synthesis, absorption, and excretion might be recognized. But 

 endless difficulties would arise as to whether hydrochloric acid is 

 synthesized or results from a local change of hydrogen ion concen- 

 tration; or whether hemorrhage is excretion or decomposition. 

 For a limited variety of species the structures concerned as paths 

 may furnish divisions, but in general, redistributions and trans- 

 formations do not commonly pass over defined morphological 

 routes. 



(4) Attempts to compare components according to the toler- 

 ated load of each can hardly be recommended at present. If I 

 were able to choose one criterion of survival and one unit for all 

 loads that are to be compared, this classification might be carried 

 out quantitatively (table 40). There is no implication that a large 

 permitted load is "better" for the organism than a small one; that 

 is a matter for further study in the light of each selected criterion. 



(5) Quantitative classification might depend on accuracy of 

 preservation of constancy for diverse components. Then values 

 of C.V. or of CA. for content of each component would be ascer- 

 tained in particular ranges of conditions (as in tables 12 and 39). 

 The time periods and physiological states chosen are strikingly 

 arbitrary. 



(6) Rates of net recovery might be compared (table 40). Oc- 

 casionally a single component would fall into very different classes 

 in diverse species, upon this criterion. 



I prefer to handle regulations by a combination of classifica- 

 tions (2) and (6). An evaluation of recoveries by those methods 

 condenses much biological information. I find it very unsatisfac- 

 tory to classify regulations according to chemical, physical, and 

 anatomical categories. Anatomical considerations are of no help 

 in protozoa. Those considerations put similar components into 

 diverse classes in organisms of different structure. They separate 

 for one component the gains from the losses, and one path of gain 

 from another. Such categories detract from the characterization 

 of adjustments and their kinetic aspects, and I think immediate 

 progress in unravelling regulations depends in part upon ignoring 

 them. 



