The Conditions of Life and Death. 89 



mean that form of death which is brought about by the 

 intrusion of bacteria. Poisoning the system with their 

 waste products, choking the blood-vessels, causing fatal 

 lesions, setting up inflammation in many ways these 

 intruders cause death, which can hardly be laid to the 

 fault of the organism except in so far as its powers of 

 resistance are imperfect. 



(c) Natural death is that cessation of life which re- 

 sults from the accumulation of physiological arrears. 

 Day after day, year after year, it may be decade after 

 decade, the machinery of the living body holds out; its 

 necessary wear and tear is made good again by food 

 and in rest, but the recuperation is not always complete. 

 Especially if there has been over-stimulation, as in the 

 case of brain-cells, or over-strain, as in the case of the 

 heart, there is a slow mounting up of physiological 

 debts. In fact the living organism, unless it be a very 

 simple one, goes slowly into debt to itself. The items 

 may be infinitesimal, but the sum-total involves that 

 physiological bankruptcy which is death. 



In contrast, then, to the old view that natural death is 

 an intrinsic necessity, the modern conception, as worked 

 out by Weismann and others, regards death as incident 

 on the complex organization of the body, on the limits 

 which are set to the asexual multiplication of cells, and 

 on the occurrence of expensive processes of reproduc- 

 tion. Moreover, Weismann has argued that the length 

 of life has been, must have been, affected by the action 

 of natural selection. ' ' Worn-out individuals are not 

 only valueless to the species, but they are even harmful, 

 for they take the place of those which are sound. Hence, 

 by the operation of natural selection, the life of our hypo- 

 thetically immortal individual would be shortened by 

 the amount which was useless to the species. It would 

 be reduced to a length which would afford the most 

 favourable conditions for the existence of as large a num- 

 ber as possible of vigorous individuals at the same time." 



Thoughts of death lead on naturally to thoughts of 

 immortality, on which, in a limited sense, organic 

 the biologist has something to say. immortality. 



It was Weismann, with his characteristic habit of 



