192 LIFE OF ELIE METCHNIKOFF 



able connection between this and the intestinal 

 flora. 



The shorter the intestine, the fewer microbes it 

 contains and the longer the relative duration of life. 

 As an example, he quoted the relatively great lon- 

 gevity of birds and bats. Those animals, adapted to 

 aerial life, have to weigh as little as possible. To 

 that end, they empty their intestine very frequently 

 and this in consequence is not used as a reservoir 

 for alimentary refuse ; as it is but little developed, it 

 contains a much smaller number of microbes. The 

 longevity of flying animals is relatively much greater 

 than that of mammals with a large intestine full of 

 microbes, a constant source of slow poisoning. 



After treating the question of longevity, Metchni- 

 koff dealt with that of death. 



Living beings die, in the great majority of cases, 

 in consequence of diseases or accidents with an 

 external cause ; one involuntarily wonders whether 

 there is such a thing as " natural death," i.e. arising 

 exclusively from causes due to the organism itself. 

 A review of known facts allowed Metchnikoff to draw 

 the following conclusions : unicellular inferior beings 

 have no natural death ; they merely die by accident. 

 Their individual life is very short and comes to an 

 end by multiplication or division of a unit into two ; 

 there is no trace of a corpse in this loss of previous 

 individuality. 



Among superior plants, certain trees attain con- 

 siderable dimensions (dragon-tree, baobab, oak, 

 cypress), live for centuries, and die from external 

 causes. Their organism presents no internal necessity 

 for a natural death. On the other hand, a multitude 

 of other plants have but a short life and their natural 



