258 SUSCEPTIBILITY AND IMMUNITY. 



completely filled with the pathogenic microorganisms that it is diffi- 

 cult to believe that they have all been picked up by a voracious pha- 

 gocyte, which has stuffed itself to repletion, while numerous other 

 leucocytes from the same source and in the same microscopic field of 

 view have failed to capture a single bacillus or micrococcus. More- 

 over, the staining of the parasitic invaders, and the characteristic ar- 

 rangement of the ' ' gonococcus " in stained preparations of gonorrhoeal 

 pus, indicate that their vitality has not been destroyed in the interior 

 of the leucocytes or pus cells, and we can scarcely doubt that the 

 large number found in certain cells is due to multiplication in situ 

 rather than to an unusual activity of these particular cells. But in 

 certain infectious diseases, and especially in anthrax, the bacilli in- 

 cluded within the leucocytes often give evidence of degenerative 

 changes, which would support the view that they are destroyed by 

 the leucocytes, unless these changes occurred before they were picked 

 up, as is maintained by Nuttall and others. We cannot consider 

 this question as definitely settled, but, in view of the importance 

 attached to the theory of phagocytosis by many pathologists and bac- 

 teriologists, we reproduce here a paper by Metschnikoff in which his 

 views are fully set forth : 



LECTURE ON PHAGOCYTOSIS AND IMMUNITY. 1 



It is not possible to study the bacteriology of disease without noticing 

 that, while ^n many cases the invading microorganisms are to be found 

 solely in the fluids of the body, in not a few affections they present them- 

 selves in the interior of certain cells, and this either partially some being 

 within the cells, others free in the blood plasma and the lymph that bathes 

 the various tissues or exclusively, all the bacteria that are visible being 

 intracellular. Many of the facts bearing upon the terms of this relationship 

 between tissue cell and microorganism are now well known, yet it is worth 

 while to recapitulate the more important, in order to show that from them it 

 is possible to gain a general law ; and what is more, that from a study of 

 such facts some insight may be gained into the phenomena of immunity. 



It may, in the first place, be postulated that whenever a microorganism 

 is discoverable within a cell its passage thither has been by means of proto- 

 plasmic or amoeboid movements, either on the part of the microbe or of the 

 cell itself. The first alternative is the rarer, although it certainly exists, and 

 of this the malarial parasite affords an excellent example ; for here in the 

 amoeboid stage of its existence the hsematozoon makes its way into the in- 

 trrior of a cell that possesses no active movements of its own, namely, the 

 red blood corpuscle, and from the substance of this corpuscle the parasite 

 gains its nourishment. Other sporozoa furnish instances almost equally 

 good. More commonly, however, as in the case of all bacteria, where we 

 have to deal wit h microorganism* which, even when mobile, are destitute of 

 protoplasmic appendages, it is the cells which play the active part ; certain 

 cells include the parasites. Of such the amoebifonn leucocyte of the blood 

 and lymph is the most typical example, capable, as it is, of sending out 

 pseudopodia in all directions, while a closely allied form is the cell of the 



1 Delivered at the Institut Pasteur, December 29th, 1890, by Dr. Elias Metschni- 

 koff, Chef de Service do 1' Institut Pasteur, Paris ; late Professor of Zoology in the 

 University of Odessa. 



