PHASES IN THE LIFE OF THE INDIVIDUAL 683 



be of no value or utility to the race, but rather a disadvantage, 

 since it would tend to retard the evolution of more perfectly 

 adapted forms of life. Furthermore, according to Weismann, 

 longevity, although depending ultimately upon the physiological 

 properties of the cells, is capable of adaptation to the conditions 

 of existence, and consequently is influenced by natural selection 

 just in the same way as other specific characters are. 



Perhaps the most cogent criticism of Weismann 's doctrine of 

 immortality is that of Verworn, who writes as follows : ' The 

 conception of living substance as immortal will be accepted by 

 scarcely any one who bears in mind the characteristic peculiarity 

 of living substance, viz., that it continually decomposes, or, in 

 other words, dies. There is no living substance that, so long as 

 it is living at all, is not continually decomposing in some parts, 

 while being regenerated in others. No living molecule is spared 

 this decomposition : the latter, however, does not seize upon 

 all molecules at the same time ; while one is decomposing, 

 another is being constructed, and so on. One living particle 

 affords the conditions for the origin of another or several others, 

 but itself dies. The particles newly formed in turn give rise 

 to others, and, likewise, die. In this manner living substance 

 is continually dying, without life itself becoming extinct." 1 

 From this standpoint, therefore, there can be no question of 

 any kind of living substance being truly immortal. The whole 

 conception of a possible immortality arises from a confusion of 

 ideas. 



Minot, 2 on the other hand, has elaborated a theory of 

 senescence which may be regarded as an extension of that 

 of Weismann. Like the latter, he seems to assume that 

 death is not a universal accompaniment of life, and that 

 natural death has been acquired in the course of evolutionary 

 development. He proceeds to define senescence as an increase 

 in the differentiation of the protoplasm. During the early 

 periods of life the young material is produced, and the proto- 

 plasm is undifferentiated. During the later stages of existence 

 cell differentiation goes on, and the organism gradually becomes 

 old. When the cells acquire the faculty of passing beyond the 



1 Verworn, General Physiology, Lee's Translation from the second German 

 Edition, London, 1899. 2 Minot, loc. cit. 



