Elias Mecznikow. 



lv 



respectively). The pathological laboratories were full of observations and talk 

 about the " diapedesis " and " out-wandering " of the amoeboid corpuscles in 

 inflamed tissues, the origin of pus corpuscles, and the activity of the amoeboid 

 cells in the stellate cavities of the frog's cornea and other connective tissues 

 when stimulated. Metchnikoff put two and two together, and formulated the 

 proposition that in all multicellular animals the main function of the cells 

 derived from the deep or mid-embryonic layer between the dermal and 

 intestinal lining layers is (with exception of those which become " muscular 

 cells ") nutritional, and that they possess the power of ingesting and digesting 

 — as does an amoeba — solid particles, whether such particles are introduced 

 from the outside or are parts of the organism which, owing to one reason or 

 another, must be broken up and removed. The amoeboid cells in connective 

 tissues and in the blood and lymph are such eater-cells or phagocytes, as he 

 now termed them. 



•He at once proceeded to explain the significance of these phagocytes and 

 their utility to the organism, not only by pointing to their work as scavengers 

 removing injured and dead tissue, to which they are brought in hundreds of 

 thousands by the process known as inflammation, but he also immediately 

 gave first-class importance to their recognition by connecting them with 

 Pasteur's great discoveries as to the cause of infective diseases by poisonous 

 f microbes " which intrude into previously healthy organisms. He further 

 connected his generalisation with Darwin's theory of the origin of species 

 by the natural selection of favoured races in the struggle for existence. He 

 published in 1884 an essay entitled ' The Struggle of the Organism against 

 Microbes,' in which he maintained the thesis that the phagocytes, universally 

 present in multicellular animals, have been developed and established by 

 natural selection in the animal organism as a protection against intrusive 

 disease-causing bacteria. 



He was able in 1884 to observe and give illustrative drawings of a 

 demonstrative case of the activity of the phagocytes in the blood of a 

 transparent fresh-water flea (Daphnia) when it was infected by a yeast-like 

 parasite called Monospora. This parasite frequently makes its way into 

 the blood of the water flea and, multiplying there, often causes death. 

 Metchnikoff watched with his microscope and made careful drawings of the 

 phagocytes as he saw them in the living flea engulfing and digesting the 

 intrusive Monospora. In some cases the phagocytes, in others the Mono- 

 spora, got the upper hand. Later, when I knew him, he had a small 

 aquarium dedicated to the cultivation of these demonstrative water fleas and 

 their infective microbe. 



Having now determined to give up his zoological and embryological 

 researches in order to devote the rest of his life to the development of his 

 doctrine of " phagocytosis," Metchnikoff accepted the invitation to become 

 director of a new bacteriological laboratory at Odessa, but, finding the 

 conditions there not favourable to his special work, he relinquished the post 

 in 1888 and, having fortunately been cold-shouldered in Berlin, came to 



