170 LIFE OF ELIE METCHNIKOFF 



plicity ; he knew their mode of defence by ingestion 

 and intracellular digestion. Having become familiar 

 with these phenomena, visible in the single cell, he 

 was better able to see his way in the complicated 

 milieu of higher beings. He was therefore able to 

 discover the connection between the divers factors 

 which other scientists had observed singly. He was 

 able to prove that it is the combination of these 

 factors, i.e. inflammation, the ingestion of living and 

 virulent microbes, and their disappearance by means 

 of intracellular digestion which makes immunity 

 possible. He demonstrated that " there is but one 

 permanent element in natural or acquired immunity, 

 and that is phagocytosis." 



The extension and importance of this factor, 

 applicable to the whole animal kingdom, proved the 

 truth and general scope of the phagocyte doctrine 

 of immunity. 



In 1900, Metchnikoff presented to the Inter- 

 national Congress in Paris a complete tabulation of 

 his researches and fought his contradictors for the 

 last time, after which, convinced that his deductions 

 were solid, he began to write a work on Immunity in 

 Infectious Diseases. In it he epitomised, as in a great 

 harmonious chord, the results of his researches, reach- 

 ing over a period of nearly twenty years ; he affirmed 

 and gave final expression to his doctrine of immunity, 

 based on the comparative study of the mechanism of 

 that phenomenon and of its evolution along the whole 

 scale of living beings ; he related his controversies, 

 analysed the objections to his doctrine, expounded 

 the theories of other scientists concerning immunity, 

 and gave a general view of the present state of 

 the question. This book is a living picture of a 



