LIFE OF ELIE METCHNIKOFF 183 



cells of our organism and thus provoke their gradual 

 weakening. He then indicated the means of combat- 

 ing this evil, on the one hand by stimulating the vital 

 activity of the cells exposed to enfeeblement, by 

 means, for instance, of small doses of specific cyto- 

 toxins, and, on the other hand, by direct action on 

 intestinal microbes. He concluded by saying that 

 " the intestinal flora is the principal cause of the 

 too short duration of our life, which flickers out 

 before having reached its goal. Human conscience 

 has succeeded in making this injustice obvious ; 

 Science must now set to work to correct it. It will 

 succeed in doing so, and it is to be hoped that the 

 opening century will witness the solution of this great 

 problem." 



Metchnikoff considered that our chronic poisoning 

 by intestinal microbes weakens our cellular elements ; 

 he supposed that the same cause might provoke 

 senile phenomena, manifestly due to weakness of the 

 tissues. 



One of the first manifestations of senility being the 

 whitening of hair, he began to study the mechanism 

 of that. He had previously observed the dominant 

 part played by phagocytosis in all phenomena of 

 atrophy, and it occurred to him that it may be phago- 

 cytes which destroy the colouring matter of hair, a 

 substance which, in the form of tiny granules, is 

 enclosed within the hair cells. In fact, he found 

 that the whitening process is accompanied by a 

 stimulation of the amoeboid cells which introduce 

 their protoplasmic prolongations into the periphery 

 of the hair. They absorb the coloured granules, or 

 pigment, and digest it, partly on the spot, partly 

 after carrying it into the root of the hair, often even 



