OLD AGE AND DEATH 85 



nourishing the same. We may sum this up by saying 

 that the individual is only a necessary incident in the 

 life-history of the germ-cells. 



The duration of life in the individual varies exceed- 

 ingly, and we know nothing of the laws that deter- 

 mine it. Great differences exist in the longevity of 

 different forms of organisms; some may live for a 

 thousand years, others for a few brief days, and some 

 again may have their life's span measured by a few 

 brief minutes. 



In spite of the fact that Old Age and Death has been 

 a topic of absorbing interest in all ages, too little atten- 

 tion has been paid to the phases of senescence to give 

 us a clear understanding of them, and thus of natural 

 death. 



Various theories have been expounded. We find 

 natural death said to be the result of arterial sclerosis 

 or of some other form of disease. Again, it has been 

 defined as that cessation of life which results from the 

 accumulation of physiological arrears. Two of the more 

 recent theories are those of Minot and of Metchnikoff, 

 who respectively declare that death is the result of 

 cellular differentiation, and that it is due to the increasing 

 activity of phagocytes. 



There seems to be a grain of truth in all the three 

 views last mentioned. The more highly differentiated 

 and specialised the cells become, the less independent 

 they become, and the more liable are they to fall into 

 a semi-poisoned condition and thus form an easy prey 

 for the phagocytes. 



If natural death, then, be the outcome of old age, no 



