BY I^. GREIG SMITH. 159 



particle.^' In the case of pathogenic bacteria that resist the 

 leucocytes, there must be something in or on the cells, or given 

 out by them, of a leucocyte-repelling (negative chemotaxic) nature. 

 What this is we do not at present know, but it is likely that 

 there is much the same physical relation between the leucocyte 

 and the capsule of the pathogenic microbe as there is between 

 water and fat, so that if the capsule is partly digested by a cytase 

 or covered with a layer of some substance which will annul the 

 repelling influence, the bacterium will be mechanically absorbed 

 by the leucocyte. 



It is possibly here that agglutination enters actively into the 

 arena of immunity. We know that bacteria, ^.(7., typhoid, which 

 have been treated with the aggiutinine contained in patient's 

 serum, become immobilised and gather into clumps through the 

 formation and flocculation of a precipitate upon the capsules. 

 We also know that after a time the bacteria regain their motility. 

 The simplest reason to account for the reassumption of mobility is 

 that the precipitate is slowly dissolved. The solubility of the 

 covering would enable the microbe to be absorbed by the leuco- 

 cyte! in the same way that a covering of shellac would enable a 

 fragment of glass to be seized by a drop of chloroform. When 

 the bacterium is within the protoplasm of the phagocyte, there 

 ought to be an increased production of immune bodies. The 

 reason for the precipitation of an albuminoid by a specific preci- 

 pitin is doubtless to be found in the fact that the albuminoid 

 is non-diffusible and does not get within the phagocyte. But 

 what does get in contact with the surface of the cell calls forth 

 a precipitin which c<'agulHtes the non-diffusible and foreign 

 albuminoid. The coagulated particles are then rapidly engulfed 

 by the phagocytes and are digested with a greater rapidity than 

 would otherwise have been the case. 



* The purely physical nature of the movements and swallowing powers of 

 amoebas are well described in Journ. App. Micros, v. 1597. 



t The subject is under investigation. 



