194 LIFE OF ELIE METCHNIKOFF 



Among human beings natural death is extremely 

 rare. It sometimes occurs in very old people, under 

 the shape of a peaceful last sleep. The likeness it 

 bears to sleep is so striking that Metchnikoff thought 

 himself authorised to form the following hypothesis 

 concerning the analogy in their mechanism. 



According to a theory of Preyer's, fatigue and sleep 

 are due to a periodical auto-intoxication set up by 

 the products of the vital activity of our organism. 

 These products are destroyed by oxidation during 

 sleep, after which fatigue disappears and awakening 

 comes. According to Metchnikof! it may be that the 

 mechanism of natural death also consists in an auto- 

 intoxication by the progressive accumulation of toxic 

 products during the whole of life. The analogy be- 

 tween sleep and natural death allows the supposition 

 that, as before going to sleep an instinctive desire for 

 rest is felt, in the same way natural death must be 

 preceded by an instinctive desire to die. Moreover, 

 this is confirmed by concrete examples. Thus that of 

 an old woman of ninety-three who expressed that desire 

 in the following terms to her great-nephew : " If ever 

 you reach my age, you wiU see that death becomes 

 desired just like sleep." The same thought had been 

 expressed by the biblical patriarchs who fell asleep 

 satiated with life. 



When, owing to the progress of Science, men reach 

 the development of the instinct of death, they will 

 look upon Death with the same calm as do very old 

 people, and it will cease to be one of the principal 

 causes of pessimism. It is for that reason that we 

 must learn to prolong life and to allow all men to 

 realise their complete and natural vital cycle, thus 

 ensuring their moral balance. 



