viii A PATHOGENIC BACILLUS 71 



entirely disappears ; rarely, the animal dies between 

 the end of the first and the end of the second week. 

 If the tumour of such a "chronic" animal is hard- 

 ened and examined in sections, stained first with 

 rubin and then with methyl blue, one finds numerous 

 bacilli in the tissue of the tumour. That they are 

 living can be shown by the successful cultures made 

 of the fresh tumour tissue. What is, however, re- 

 markable is that while the substance of the leuco- 

 cytes in the subcutaneous tissue at and about the 

 seat of inoculation in the acute fatal cases en- 

 closes the bacilli abundantly, there is nothing of the 

 sort to be seen in the leucocytes of the " chronic " 

 tumour. This is rather contrary to what we ought to 

 expect if the theory of phagocytosis (Metschnikoff), 

 i.e. the swallowing and destruction of the bacilli by 

 the leucocytes, were applicable here ; for it would be 

 serving no object if the leucocytes of the oedematous 

 tissue in the acute cases, were destroying them, 

 seeing that the tissue in general is flooded with 

 the bacilli, and the animals die rapidly ; whereas in 

 the " chronic " cases, if the resistance of the animal 

 were due to a salutary part played by the leucocytes, 

 to wit, acting as phagocytes : taking up and destroy- 

 ing the bacilli and thus preserving the life of the 

 animal, we should expect to find at least some of 

 the leucocytes enclosing the bacilli ; but evidence 



