192 Regulation of Size in Unicellular Organisms 



some of the interactions which have been observed. It 

 is inadequate to find that a significant correlation 

 exists between total oxygen consumption and the 

 duration of life; between amount of food ingested and 

 the size of the body at maturity. The existence of one 

 correlation does not indicate the mechanism of causa- 

 tion. The essential problem lies in the quantitative 

 interaction of all the factors whose resultant is the 

 phenotypical realization of a genotypical character. 



Partial factors. One picture of the interacting fac- 

 tors that might be derived from the facts which have 

 been set forth in these chapters is somewhat as follows. 

 Every individual is a member of a chain of generations 

 which are succeeding one another at regular intervals 

 of time. Assimilation is the chief activity of each or- 

 ganism; this activity is punctuated periodically by fis- 

 sioning. But the fissions occur not merely after the 

 passage of so much time but rather after the passage 

 of certain quantities of certain activities. Each of 

 these activities is compounded of many physiological 

 functions; so that it is necessary to correlate not 

 merely so much assimilation, not merely so much res- 

 piratory metabolism, but also so much pressure of 

 oxygen, so much tension of acid, so much mass activi- 

 ty of incoming food materials. Each of these constitu- 

 ent functions and their like is in turn modified by tem- 

 perature, diffusing capacity, locomotion, reorganiza- 

 tion, and other characteristics. 



How shall these correlatives be evaluated? Evi- 

 dently each must be treated, for a specific clone of or- 

 ganisms, in the manner that size has been evaluated. 

 Instead of having a few data upon fission rate in one 

 clone under one set of conditions, upon oxygen con- 

 sumption in another species under a second set of con- 

 ditions; some ten or twenty activities must be meas- 

 ured in relation to some one or two or more condi- 



