44 BIOLOGY OF DEATH 



basic idea have been presented by Jickeli and Montgom- 

 ery. Both held that because of the mechanical incomplete- 

 ness of the processes of metabolism, injurious and toxic 

 substances tend to accumulate in the cells of the body, 

 and that senescence and death are the results of 

 such accumulations. 



A much broader, and in the light of all facts sounder 

 view, is that the determination of degrees of longevity 

 and of the fact of death itself, is inherent in the innate, 

 hereditarily determined biological constitution of the in- 

 dividual and the species. This view was expressed by 

 Johannes Miiller a quarter of a century ago in his Plfiysi- 

 ologie, by Cohnheim forty years later, and has had many 

 later adherents. I shall return to a discussion of it later. 



There have been a number of theories of senescence 

 and death, differing widely in details, but having the one 

 point in common of attributing these phenomena to 

 orderly changes with advancing age in the relative pro- 

 portion of nucleus to protoplasm in the cells of the body. 

 Here may be mentioned, without pausing to go into de- 

 tailed consideration of their different views, Verworn, 

 Miihlmann, Eichard Hertwig, and Minot. 



Another group of hypotheses, all advanced in com- 

 paratively recent times and associated with the names of 

 Kassowitz, Conklin, and Child, are developed about the 

 metabolic aspects of age changes. There is observed a 

 decrease in assimilatory capacities of cells with differen- 

 tiation and age. These metabolic changes are regarded 

 as fundamentally casual of the phenomena of senescence 

 and death. In this general group of hypotheses would 

 belong the views of my colleague, Dr. W. T. Howard. 



Benedict in a detailed investigation of senility in 

 plants reaches the conclusion: 



