vii THE STAGES OF LIFE AND DEATH 315 



these lead logically to the conclusion that the fatal arrest of the 

 cerebral functions must precede that of the cardiac functions, with 

 which life finally ends. The brain, the culminating point of 

 animal life, is the primum moriens ; the heart, the central organ 

 of vegetative life, is the ultimum moriens. 



X. We have already pointed out that Metschnikoff, in his 

 doctrine of pathological senility, regards natural death as a great 

 rarity, as potential rather than actual. Should the prophylaxy 

 suggested by him be successful and the presumed morbid state of 

 old age thereby be prevented, natural death, which is now the 

 exception, would obviously become the rule. 



In support of his theory Metschnikoff looked for analogies in 

 the animal world, where, however, he believes natural death to be 

 somewhat rare. He found one example of natural death in a 

 species of orthoptera, the ephemera, which only lives a few days, 

 and undergoes no change which can be regarded as an internal 

 cause of death. It has, however, lost the instinct of self-preserva- 

 tion, since the adult insects allow themselves to be caught without 

 making the slightest attempt at escape, as other insects would do. 

 He regards this behaviour as a phenomenon connected with 

 natural death, and considers that this loss of the will to live would 

 be noted in the old of the human species if they really died a 

 natural death. He remarks that on the contrary the diminution 

 and cessation of the instinct of life are very seldom seen ; the 

 greater number of old people wish to prolong their lives, dread 

 death, and seek every means of postponing it. This instinct of 

 preservation, this desire to live, has been handed down by an 

 infinite number of generations, and is consequently very wide- 

 spread and tenacious. We can hold with Darwin and his 

 followers that those who have not looked on life as a benefit have 

 been gradually eliminated before giving birth to others. To the 

 survivors and their progeny life, though not devoid of sorrow, 

 trouble, and evil, is a source of delight; and when they grow 

 old, the memory of bygone joys, the fear of the unknown beyond, 

 the dread of non-existence, make them cling fast to life and regret 

 the happiness past, even when there is a sense of weariness and 

 suffering, and when the truth of Leopardi's dreary conviction of 

 " the infinite vanity of all things " is borne in upon the soul. 



Metschnikoff strives to mitigate this tormenting doubt as to 

 the value of human life, and to exalt the instinct which cherishes 

 it ; unfortunately, however, most of the grounds upon which he 

 bases his new optimism are purely theoretical. The necessity of 

 dying and the desire for death as a deliverance are not readily con- 

 ceivable in physiological old age, which presupposes a long life of 

 comparative happiness. Metschnikoff tries with his theories to 

 give mankind the possible prospect of a voluntary and happy end 

 to bodily existence, instead of the actual ordinary end, which is 



