From the very first, Pasteur sympathised with the phagocyte theory; the other members of the Institute thought it too biological, almost vitalistic. But when they had made themselves thoroughly cognisant with it, they also adopted it. Thus, having found in the Pasteur Institute not only favourable working conditions but also moral support, Metchnikoff became deeply attached to it, and the interests of "the House" became his.
In 1915, on the occasion of Metchnikoff's seventieth anniversary, M. Roux, in a Jubilee speech, gave of him and of his work the following appreciation which describes, better than anything I could say, what his part was in the Pasteur Institute:
In Paris as in Petrograd, as in Odessa, you have become a leader of thought, and you have kindled in this Institute a scientific focus which has radiated afar.
Your laboratory is more alive than any in the house; workers come to it in crowds. There, the bacteriological events of the day are discussed, interesting preparations examined, ideas sought for that may help an experimenter to solve difficulties in which he has become involved. It is to you that one comes to ask for a control experiment on a newly observed fact, for a criticism of a discovery that does not always survive the test.
Moreover, as you read everything, every one comes to you for information, for an account of a newly published memoir which there is no time to read. It is much more convenient than to consult the library and also much safer, for errors of translation and interpretation are avoided.
Your erudition is so vast and so accurate that it is made use of by the whole house. How many times have I not availed myself of it? One never fears to take advantage of it, for no scientific question ever finds you indifferent. Your ardour warms the indolent and gives confidence to the sceptical.
You are an incomparable collaborator as I know, I who have had the good fortune of being associated with your researches on several occasions. Indeed, you did nearly all the work!
More even than your science, your kindliness attracts; who amongst us has not experienced it? I have had a touching proof of it when, many times, you have nursed me as if I were your own child. You are so happy in doing good that you even feel gratitude towards those whom you serve.