INFECTION AND IMMUNITY. 91 



future investigation of such diseases as scarlet fever, measles, 

 smallpox, rabies, etc., which, though unquestionably of 

 microbic origin, have so far failed to reveal any specific germ 

 for their causation. 



QUESTIONS. 



Why are animals inoculated ? 



What different methods are used for animal inoculation in the laboratory ? 



Describe the subcutaneous method. The intravenous method. The intra- 

 lymphatic method. The intraperitoneal method. 



What instruments are used to inoculate liquid cultures into the veins of 

 animals ? 



What should be observed in inoculated animals ? 



How should an autopsy be made in the case of an animal dead after 

 inoculation ? 



What precautions are necessary in making cultures from tissues and organs 

 in dead animals to prevent contamination from outside ? 



How should secretions of animals and men be collected for bacterial exam- 

 ination ? 



What form of culture have Eoux and Nocard proposed for cultivation of 

 bacteria ? 



CHAPTER VII. 

 INFECTION AND IMMUNITY. 



INFECTION. 



BACTEEIA which produce diseases in animals and man are 

 known as the pathogenic bacteria, and the process by which 

 disease is produced is called infection. 



The mode of communication of these infections to man or 

 to animals is not fully demonstrated. The following explana- 

 tions are the more plausible. 



The Theories of Infection. 



1. The rapid multiplication of bacteria in the blood and 

 organs of infected animals is supposed to interfere with their 

 bodily functions, and so cause disease and death. This is the 

 so-called mechanical theory of infection, and finds support in 

 such diseases as anthrax, when in fatal cases every capillary 



