98 BIOLOGY OF DEATH 



till at the far end of the bridge we see only the gray- 

 beard and the 'lean and slippered pantaloon.' As they 

 pass along the causeway the throng is more and more 

 thinned ; five Deaths are posted at different stages of the 

 route longside the bridge, and with different skewness 

 of aim and different weapons of precision they fire at 

 the human target till none remains to reach the end of the 

 causeway — the limit of life." 



This whole, somewhat fanciful, conception of Pear- 

 son's needs a little critical examination. What actually 

 he has done is to get a good empirical fit of the dx line 

 by the use of equations involving all told some 17 con- 

 stants. Because the combined curve fits well, and funda- 

 mentally for no other reason, he implicitly concludes 

 that the fact that the fit is got by the use of five compo- 

 nents means biologically that the dx line is a compound 

 curve, and indicates a five-fold biological heterogeneity in 

 the material. But it is a very hazardous proceeding to 

 draw biological conclusions of this type from the mere 

 fact that a theoretical mathematical function or functions 

 fits well a series of observational data. I fully discussed 

 this point several years ago and pointed out : 



"The kind of evidence under discussion can at best 

 have but inferential significance; it can never be of de- 

 monstrative worth. It is based on a process of reasoning 

 which assumes a fundamental or necessary relationship 

 to exist between two sets of phenomena because the same 

 curve describes the quantitative relations of both sets. 

 A little consideration indicates that this method of rea- 

 soning certainly cannot be of general application, even 

 though we assume it to be correct in particular cases. 

 The difficulty arises from the fact that the mathematical 

 functions commonly used with adequate results in physi- 



