64 PATHOGENIC BACTERIA. 



food-particles, and sometimes between ameboid cells and 

 inert particles. This attractive force, when operating so 

 as to draw the ameba to the particle it will devour, is 

 further named positive chemotaxis in order to distinguish 

 it from a repulsive force sometimes exerted causing the 

 ameboid cells to fly from an enemy, as it were, and which 

 is called negative chemotaxis. 



The force that operates and guides the ameba in its 

 movements is exactly the same as that which governs the 

 movement of the phagocytic cells of the human body, 

 and observation of these phenomena is not difficult. If 

 a small capillary tube be filled with sweet oil and placed 

 beneath the skin, only a short time need pass before it 

 will be found full of leucocytes positive chemotaxis. 

 If, instead of sweet oil, oil of turpentine be used, not 

 a leucocyte will be found negative chemotaxis. 



Phagocytosis is almost universal in the micro-or- 

 ganismal diseases at some stage or another. If the 

 blood of a patient suffering from relapsing fever be 

 studied beneath the microscope, it will be found to 

 contain numerous active mobile spirilla, all free in the 

 liquid portion of the blood. As soon as the apyretic 

 stage comes on not a single free spirillum can be found. 

 Every one is seen to be enclosed in the leucocytes. 



At the edge of an erysipelatous patch a most active 

 warfare is waged between the streptococci and the cells. 

 Near the centre of the patch there are many free strep- 

 tococci and a few cells. At the margin there are free 

 streptococci, and also a great many streptococci en- 

 closed in cells (leucocytes) which are, for the most part, 

 dead. In the newly-invaded tissue we find hosts of 

 active living cells engaged in eating up the enemies 

 as fast as they can. The phagocytologists tell us that at 

 the centre the bacteria are fortified, actively growing, and 

 virulent ; in the next zone the leucocytes which have 

 feasted upon the bacteria are poisoned by them ; outside, 

 the cells, which are more powerful and which are con- 

 stantly being reinforced, are waging successful warfare 



