68 BIOLOGY OF DEATH 



upon the second of these conclusions? So far our evi- 

 dence in its favor has been indirect and inferential, 

 though cogent so far as it goes. In this connection, a 

 paper of Friedenthal's is of considerable interest. He 

 shows that there is a marked correspondence between the 

 longevity of various species of animals and a constant 

 of organization which he calls the ' ' cephalisation factor. ' ' 

 This cephalisation factor in pure form, in his sense, is 

 given by the equation. 



, ,. ,. e Brain weight 

 Cephalisation factor = . 2 - t 



Total mass of body protoplasm. 



Now " total mass of body protoplasm," as distinct from 

 supporting structures, such as bone etc., is obviously 

 difficult to determine directly. But Friedenthal is well 

 convinced that, to a first approximation, the cephalisa- 

 tion factor may be written in this way: 



-, , ,. ,. . Brain weight 



Cephalisation factor = -r^ -, ?__ 2 A 



(Body weight) ' 



Computed upon the latter basis he sets up tables of the 

 relation between cephalisation factor and longevity for 

 mammals and for birds. It is not necessary to repro- 

 duce here the long tables, but to show the general point, 

 the following table for five selected species of mammals 

 will suffice: 



TABLE 5 



Relation between the cephalisation factor and longevity (Friedenthal) 



There appears in this short selected table a defect 



