68 BIOLOGY OF DEATH 



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

 dence in itsi favor has been indirect and inferential, 

 thougli 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. 



„ , ,. i- r i. Brain weight 

 Cephalisation factor = _ . ^ — v- 



' 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: 



Cephalisation factor = g^g^^g^^^ H 



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 



