R e a d b efore the A la m ed a C ou nty D is tr ic t D en tal A s s o c ia tio n , O akland, C a lif., D ecem ber 5th, 19X6.) A S E A R L Y as 1870 certain biolo gists noticed the presence of micro organisms within the cells of both animal and human tissues. A little la ter, several observers noticed that som? leucocytes contained bacteria, but did not interpret it as a means of protection, but rather as a means of transporting the bacteria thru the infected body. It remained for Metchnikoff

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... 1883 to give to the world the result of his observations, in which he claimed that the leucocytes acted as protectors of the animal organism, that they ingested, and digested bacteria which had invaded the animal economy, acting as phagocytes or scavengers. He compared this pro cess of cell ingestion, or phagocytosis of foreign particles, to that taking place in the protozoa. In the Amoeba for in stance, the simple jelly like mass of protoplasm moves by means of the pseudopodia toward its food, engulfs it, digests it, and moves on, leaving an in digestible portion. In. Sponges, and in the Coelenterates, individual cells still perform the function of taking up food particles and digesting them, but as we come up in the scale of life, we find that cells become more specialized, and the digestion of food takes place in the cavity of the stomach and intestine, with the help of various digestive juices which are poured . upon it. While cer tain specialized cells take care of the nutritive function, other cells develop the function of protectors of the animal from invasion by microorganisms which will produce disease unless overcome. It is to these cells that Metchnikoff has given the name of phagocytes. From what has been said of the Amoeba, Sponges and Coelenterates, you can readily see that the phagocytic cells of man are descendants of cells whose normal function was to digest intra-cellularly, and thru them we still possess this method of digestion side by side with the extra cellular digestion which occurs in our stomach and intestine. At the time when Metchnikoff began his study ,of this subject, pathologists held very complicated views of inflam mation, which involved complex coor dinated reactions of vascular and ner vous systems, and his primary purpose 889