TO MESSIEURS E. DUCLAUX AND E. ROUX. 



My dear Friends, 



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

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

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

 my task 



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

 work alongside the venerated Master who founded the House where 

 we have 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 knowledge, 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. 



METCHNIKOFF. 



Institut Pasteur, 



3 October, 1901. 



