August 24, 1906.] 



SCIENCE. 



231 



puscles swallowing and digesting the 

 spores of a parasitic fungus which had 

 attacked the water-fleas and was causing 

 their death. He came to the conclusion 

 that this is the chief, if not the whole, 

 value of these corpuscles in higher as well 

 as lower animals, in all of which they are 

 very abundant. It was known that when 

 a wound bringing in foreign matter is in- 

 flicted on a vertebrate animal the blood- 

 vessels become gorged in the neighborhood 

 and the colorless corpuscles escape through 

 the walls of the vessels in crowds. Their 

 business in so doing, Metchnikoif showed, 

 is to eat up the foreign matter, and also to 

 eat up and remove the dead, wounded tissue. 

 He, therefore, called these white or color- 

 less corpuscles 'phagocytes,' the eater-cells, 

 and in his beautiful book on 'Inflamma- 

 tion,' published twenty years ago, proved 

 the extreme importance of their activity. 

 At the same time he had shown that they 

 eat up intrusive bacteria and other germs; 

 and his work for the last twenty years has 

 mainly consisted in demonstrating that 

 they are the chief, and probably the only, 

 agents at work in either ridding the human 

 body of an attack of disease-causing germs 

 or in warding off even the commencement 

 of an attack, so that the man or animal in 

 which they are fully efficient is 'immune' 

 — that is to say, can not be effectively at- 

 tacked by disease-germs. 



Disease-germs, bacteria or protozoa pro- 

 duce poisons which sometimes are too much 

 for the phagocytes, poisoning them and so 

 getting the upper hand. But, as Metchni- 

 koff showed, the training of the phagocytes 

 by weak doses of the poison of the disease- 

 germ, or by weakened cultures of the dis- 

 ease-germ itself, brings about a power of 

 resistance in the phagocytes to the germ's 

 poison, and thus makes them capable of 

 attacking the germs and keeping them at 

 bay. Hence the value of inoculations. 



The discussion and experiments arising 

 from Metchnikoff's demonstrations have 

 led to the discovery of the production by 

 the phagocytes of certain exudations from 

 their substance which have a most impor- 

 tant effect in weakening the resistance of 

 the intrusive bacteria and rendering them 

 easy prey for the phagocyte. These are 

 called 'sensitizers,' and have been largely 

 studied. They may be introduced artifi- 

 cially into the blood and tissues so as to 

 facilitate the work of the phagocytes, and 

 no doubt it is a valuable remedial measure 

 to make use of such sensitizers as a treat- 

 ment. Sir A. E. Wright considers that 

 such sensitizers are formed in the blood 

 and tissues independently of the phago- 

 cytes, and has called them 'opsonins,' 

 under which name he has made most valu- 

 able application of the method of injecting 

 them into the body so as to facilitate the 

 work of the phagocytes in devouring the 

 hostile bacteria of various diseases. Each 

 kind of disease-producing microbe has its 

 own sensitizer or opsonin; hence there has 

 been much careful research and experiment 

 required in order to bring the discovery to 

 practical use. Metchnikoff himself holds 

 and quotes experiments to show that the 

 'opsonins' are actually produced by the 

 phagocytes themselves. That this should 

 be so is in accordance with some striking 

 zoological facts, as I pointed out nearly 

 twenty years ago. For the lowest multi- 

 cellular animals provided with a digestive 

 sac or gut, such as the polyps, have that 

 sac lined by digestive cells which have the 

 same amoeboid character as 'phagocytes,' 

 and actually digest to a large extent by 

 swallowing or taking into their individual 

 protoplasm raw particles of food. Such 

 particles are enclosed in a temporary cav- 

 ity, or vacuole, into which the cell-proto- 

 plasm secretes digestive ferment and other 

 chemical agents. Now there is no doubt 



