LIFE OF ELIE METCHNIKOFF 161 



followed with the eyes, it is impossible to do so where 

 poisons are concerned, since they are invisible ; it 

 is necessary to proceed by a different road. 



Faithful to his method of taking as a starting-point 

 the simplest expression of the phenomenon to be 

 studied, Metchnikoff began by lower beings. Uni- 

 cellular organisms, such as myxomycetes, amoebae, 

 and infusoria, sometimes manifest a natural immunity 

 to certain poisons. It is also possible to endow 

 them with artificial immunity by accustoming them 

 gradually to substances which, ingested straight away, 

 would infallibly have killed them. Such phenomena, 

 seen in unicellular beings, could only be ascribed to 

 the reaction of the cell itself. Therefore Metchni- 

 koff supposed a priori that the phagocytes, being 

 similar primitive cells of multicellular beings, would 

 also react against poisons. And, in fact, he ascer- 

 tained that the number of phagocytes in a rabbit's 

 blood diminished considerably under the influence of 

 a fatal dose of arsenic, whilst it increased under the 

 influence of small doses of the poison, to which it was 

 possible to accustom the animal. 



Dr. Besredka, a disciple of Metchnikoff, made some 

 very interesting researches, which entirely confirmed 

 the share of the phagocytes in the reaction against 

 sulphides of arsenic. He had chosen the trisulphide, 

 a very slightly soluble salt of an orange colour, in 

 order to find it again easily within the organism. 

 After having injected non-fatal doses of it into the 

 peritoneal cavity, he obtained an exudate in which 

 all the orange granules of the salt were to be found 

 included within those leucocytes which have a large, 

 non-lobed nucleus the macrophages. These cells 

 gradually digested the salt they had englobed, which 



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