PHASES IN THE LIFE OF THE INDIVIDUAL 727 



cells by neuronophags, and that there are many other devouring cells 

 which are adrift in the tissues of aged men and animals and cause 

 the destruction of other cells of the higher type. The testes, however, 

 appear to have the power to resist these phagocytes, and with this 

 power is correlated the fact that spermatozoa are often produced e\en 

 in advanced old age. MetehnikofFs theory as to the cause of death 

 is that it is due to the poisoning of the tissues and to the damage 

 done by phagocytes to those parts of the body affected by the toxic 

 action. He believed further that in man and certain of the animals 

 this process of poisoning is brought about by fermentation set up by 

 microbial action in the large intestine. The toxic substances produced 

 by the intestinal fennentation were supposed to enter the system and 

 poison it, the result being that the vitality of the tissues is lowered, 

 so that they are less able to resist the action of devouring phagocytes. 

 The presence of lactic acid in the intestine was believed to arrest the 

 process of fermentation. Metchnikoff recommended, therefore, the 

 regular drinking of sour milk as a means of destroying the microbes 

 in the intestine in the hope of prolonging life. 



The term " Death " is employed in two separate senses ; it may 

 mean the death of the whole body, i.e. somatic death (this being 

 the sense in which it is ordinarily used), or it may be applied to the 

 death of the individual tissues, some of which remain alive for many 

 hours after the body as a whole is said to be dead. The death of 

 the body as a whole usually occurs suddenly. As Michael Foster 

 says : " Were the animal frame not the complicated machine we 

 have seen it to be, death might come as a simple and gradual dis- 

 solution, the ' sans everything ' being the last stage of the successive 

 loss of fundamental powers. As it is, however, deatli is always more 

 or less violent; the machine comes to an end by reason of the 

 disorder caused by the breaking down of one of its parts. Life 

 ceases not because the molecular powers of the whole body slacken 

 and are lost, but because a weakness in one or other part of the 

 machinery throws its whole working out of gear. ' 



The synchronous disturbance of two or more of the bodily 

 functions, such as is wont to occur in old age, may destroy that 

 co-ordination of the various vital activities without which life 

 cannot continue. The stoppage of the heart's beat is the ordinary 

 criterion of death, and this is a true conception, because the cessation 

 of the heart's movements implies the arrest of the circulation of the 

 blood and the consequent starvation of the tissues of the body. 



The tissues do not die simultaneously, for, as already described, 

 some cells of the body are in process of disintegration through the 

 whole of life. After somatic death, the cells which make up the 



1 Foster, '/'.,?-/,/ ,,/' /'/,,/.</-./,/,/. 1'ait IV., 5th Edition, London, 1891. 



