TO MESSIEURS E. DUCLAUX AND E. ROUX. 



My dear Friends, 



Permit me to dedicate to you this worh, which sums up 

 the labours of tiventy-five years ; a very great part of it has been 

 carried out by your side, you ivho have done so much to lighten 

 my task 



When, nearly fourteen years ago, you allowed me to share your 

 icorh alongside the venerated Master who founded the House where 

 we hojve laboured together, you were anything but partisans of 

 my theories; they seemed to you too vitalistic, and not sufficiently 

 physico-chemical. In course of time you became convinced that 

 my ideas were not without foundation, and since then you have 

 given me warm encouragement to pursue my researches in the 

 field that I had marked out for myself 



Working by your side and drawing largely from your vast 

 and varied stores of hiowledge, I felt myself safe from those diva- 

 gations into which a zoologist, who had wandered into the domain 

 of biological chemistry and of medical science, is likely to stray. 

 I thank you with all my heart, and I beg you to accept the homage 

 of this work as a testimony of my deepest gratitude and of my 

 warmest friendship. 



JELIE METCHNIKOFF. 



Institut Pasteur, 



3 October, 1901. 



