^echanism of immunity against micro-organisms 187 



The experiments of Gengou with the extracts of macrophages 

 have demonstrated, on the other hand, that this fluid exerts no 

 bactericidal power. Let it be understood at the outset that this 

 fact is in no way an indication of the absence of the bactericidal 

 ferment in the macrophages. Direct examination of the phenomena 

 which are manifested inside these cells demonstrates most clearly that 

 the macrophages kill and digest micro-organisms. But this process 

 usually goes on much more slowly in the macrophages than in the 

 microphages, owing probably in the former to the presence of a 

 smaller quantity of the bactericidal substance. Under these conditions 

 we can readily understand that this substance does not pass, or passes 

 only in small amount, into the extracts. There is nothing remark- 

 able in the fact that, with so imperfect a method of preparing the 

 extracts, the greater part of the bactericidal substance should remain 

 in the bodies of the cells. 



. The facts just set forth afford a sufficient explanation of the marked 

 difference in the results obtained by various observers as to the 

 bactericidal power of the exudations. When the latter are rich in 

 [microphages, the bactericidal property is very marked : when, on 

 the other hand, the exudations contain a large number of macro- 

 phages, the bactericidal power may be very weak or even nil. 



The experiments above summarised confirm the conclusion that [198] 

 the microphages must be regarded as the source of the bactericidal 

 substance of the body fluids. But here arises the question : Do the 

 microphages secrete the substance during life, giving it up to the 

 blood plasma, or does this substance escape only after the death of the 

 leucocytes and the damaging of the cells, due to various external 

 causes? We here touch on a problem which has been the subject 

 of much discussion and one of very great importance in connection 

 with the question of Immunity in general. 



After the discovery of the bactericidal power of serums, several 

 investigators set to work in search of the source of the bactericidal 

 substance. Hankin^, and shortly afterwards Kanthack and Hardy '^j ex- 

 pressed the view that this substance is the secretion-product of the 

 eosinophile leucocytes which would thus appear to be a kind of motile 

 unicellular glands. This theory could not be supported by solid 



1 Centralhl.f. Bakteriol. u. Parasitenk,, Jena, 1892, Bd. xii, SS. 777, 809 ; 1893, 

 Bd. XIV, S. 852. 



2 Proc. Roy. Soc. London, 1892, Vol. Lii, p. 267 ; Phil. Trans.^ Loudon, 1894, 

 (B) Vol. 185, pt. I, p. 279. 



