CHAPTER VI. 

 IMMUNITY AND INFECTION. 



GENERAL PHENOMENA OF IMMUNITY. 

 I. CLASSIFICATION OF IMMUNITY. 

 A. Natural or Inherited Im- 

 munity. 

 1. Racial. 



2. Passive Immunity. 



(a) Antibody Im- 

 munity. 

 (6) Chemotherapy. 



3. Mixed, Active and 



2. Individual. Passive Immunity. 



B. Acquired or Induced Im- j II. INFECTION PRIMARY AND SEC- 

 munity. ONDARY. 



1. Active Immunity. 



(a) Natural Ac- 

 quired Im- 

 munity. 



(6) Artificial Ac- 

 quired Im- 

 munity. 



A. Defenses of the Host, Non- 

 specific and Specific. 

 III. THEORIES OF IMMUNITY. 



A. The Humoral Side-chain or 



Ehrlich Theory of Im- 

 munity. 



B, The Metchnikoff or Phago- 



cytic Theory of Im- 

 munity. 



GENERAL PHENOMENA OF IMMUNITY. 



IT has long been recognized that man and animals exhibit refrac- 

 toriness to infection with specific bacteria or other microorganisms 

 which cause serious epizootics in closely related animals. Man is, 

 as a rule, quite free from the epizootic diseases of animals domesticated 

 by him, and the domestic animals are usually not infected with the 

 organisms which incite progressive disease in man. Thus, man does 

 not contract chicken cholera and domestic animals do not become 

 infected with the typhoid bacillus. Furthermore, closely related 

 animal species may exhibit striking differences in susceptibility to 

 the same disease; for example, field mice are readily infected with 

 the glanders bacillus, but house mice are quite resistant to infection 

 with this organism, and ordinary sheep readily succumb to anthrax 

 although Algerian sheep are practically immune to infection with the 

 anthrax bacillus. 



This inherent or congenital resistance or refractoriness to infection 

 with a specific microorganism, when general among the individuals of 

 a species or group of animals or of man is termed natural or inherited 

 immunity. It is not necessarily absolute; lowering the natural resis- 

 tance of the individual may render him susceptible to infection. Thus 



