METHODS AND CHANNELS OF INFECTION 683 



in the body fluids. Besides acting as phagocytes they may, according 

 to Metchnikoff, produce antitoxins and bactericidal substances. It 

 has been suggested that the initial leucopenia in some cases is due to the 

 production of negative chemotactic substances. Some virulent 

 bacteria cannot be phagocytized probably because they produce 

 very strong negative chemotactic substances. 



Antibody Formation. One of the general results of pathogenic micro- 

 organisms in certain infections is the production of antibodies of various 

 kinds. These may be antitoxins as in the case of tetanus and diph- 

 theria, or bactericidal substances as in typhoid fever and cholera, or 

 opsonic substances as in the pyogenic infections. Agglutinins, pre- 

 cipitins, and other bodies are also sometimes produced in conjunction 

 with the other immune substances mentioned. 



