VACCINATION. IMMUNIZATION. INOCULATION 



1. IMMUNITY, MITIGATION, AND METHODS OF 

 INOCULATION 



Immunity. — It was early observed that after recovery from 

 certain infectious diseases the animal or human body was pro- 

 tected against a new infection. This protection against infection 

 is called immunity and the animal endowed with this property of 

 insusceptibility is said to be immune or refractory to a specific 

 infection. There are different varieties of immunity. Species 

 immunity is the natural insusceptibility of an entire animal 

 species to certain infectious diseases. For example, cattle are 

 immune to glanders, the horse to lung plague and rinderpest, the 

 dog and the cat to swine erysipelas, man to fowl cholera, the rab- 

 bit to black-leg, and almost all species of animals to syphilis, 

 scarlet fever, and measles. The immunity may even be limited 

 to certain breeds of a species. The Algerian sheep, unlike the 

 other breeds, are alleged to be immune to anthrax. The German 

 native swine and the Yorkshire swine are much less susceptible 

 to erysipelas than the other breeds; compared with field mice, 

 house mice and white mice are immune to tuberculosis and gland- 

 ers. This variety of immunity is due to certain unknown proper- 

 ties peculiar to the species and breeds, Individual immunity 

 refers to the insusceptibility of single individuals of the same 

 animal species to this or that infection to which the members of 

 the species are susceptible. It is frequently observed in an out- 

 break of foot-and-mouth disease in cattle, or of contagious pneu- 

 monia, influenza and strangles of horses, that a large percentage 

 of the animals in a stable remain free from infection. 



Both of the aforementioned varieties of immunity, species 

 and individual immunity, fall under the general term of natural 

 15 225 



