CHAPTER XIV 



TYPES OF ^IMMUNITY. PREPARATION OF VACCINE. 

 ANAPHYLAXIS 



RESISTANCE to bacterial infection may be inherent or natural 

 or it may be acquired as a result of an attack of the disease or by 

 artificial means. Natural immunity is an inborn quality of a 

 species and of course is the converse of natural susceptibility; 

 acquired immunity, on the other hand, is not inborn but gained 

 during the person's lifetime. It is a state of natural susceptibility 

 transformed into one of resistance. 



Natural Immunity. This type of immunity is an inherited 

 character usually possessed by all individuals of a given species; 

 thus man is immune to certain diseases of the lower animals, 

 such as swine plague, fowl cholera, mouse septicemia, etc. On the 

 other hand, animals are immune to many of the diseases common 

 to man, such for example as measles, typhoid fever, chicken pox, 

 etc. 



Closely related species often show a marked difference in theii 

 degree of resistance to the same infection ; white mice are practi- 

 cally immune to glanders whereas field mice are highly susceptible. 

 Negroes are said to be more susceptible to tuberculosis and less 

 susceptible to yellow fever than Caucasians. In man the differ- 

 ence in racial immunity is not so marked as was formerly sup- 

 posed ; opportunities for infection and diverse hygienic customs 

 may in a large measure account for such differences. No race of 

 mankind seems to possess absolute immunity to any disease to 

 which the species is susceptible. 



Individual differences are often noticed in the degree of resist- 

 ance to infection in, for example, slight cuts and scratches. Indi- 



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