316 INFECTION AND IMMUNITY. 



ganisms. On the one hand, the secondary bac- 

 teria may produce more favorable conditions for 

 the growth of the anaerobes by consuming local 

 oxygen, or, as Metchnikoffi believes, they may so 

 engage the phagocytes that the latter have no dis- 

 position to take up the essential organism. This 

 condition may be an important one in other mixed 

 infections, as when the streptococcus complicates 

 diphtheria and scarlet fever. 



Acquired im- If the phagocytic power is an index of the de- 

 bacteria^ gree of natural antibacterial immunity, is the same 

 correspondence to be recognized when the immun- 

 ity is acquired? To answer this question satisfac- 

 torily it is necessary to bring phagocytosis in rela- 

 tion to two different types of antibacterial immun- 

 ity which it is possible to recognize. Cholera is an 

 example of that type of antibacterial immunity in 

 which the bactericidal power of the serum under- 

 goes a great increase. It is stated that anthrax 

 represents another type in which the immunity is 

 not dependent on the bactericidal power of the 

 serum. Probably the same may be said of acquired 

 immunity to the streptococcus, staphylococcus and 

 the pneumococcus, yet it is perhaps not definitely 

 established that the immunity in these instances 

 is antibacterial rather than antitoxic. For the 

 present we may, however, with Metchnikoff, con- 

 sider that the immunity is antibacterial and that 

 it is a cellular or phagocytic immunity. 

 Anthrax. Rabbits which have been immunized against 

 anthrax respond to subcutaneous or intraperitoneal 

 injection of a virulent culture by concentrating so 

 vast a number of microphages at the site of inocu- 

 lation that the fluid becomes purulent in appear- 



