PATHOGENIC BACTERIA 271 



Immunity to Pathogenic Bacteria. Immunity is resist- 

 ance to disease. The absence of such resistance characterizes 

 susceptibility. The subject of immunity in all its phases is 

 being carefully investigated at the present time by many 

 scientific workers. It is one of the most interesting of the 

 comparatively unexplored fields of science. Only a very 

 brief outline of the subject is given below. 



The following table will be serviceable as an outline : 

 Racial 



Natural 

 Immunity 



Inherited f Antitoxic 



[Active Immunity j 

 Acquired j [Antibacterial 



[Passive 



Natural immunity is the immunity which certain species or 

 races of animals and plants possess against pathogenic bac- 

 teria and other disease-producing microorganisms. For 

 example, man is immune to chicken and hog cholera, and the 

 horse is immune to typhoid fever and Asiatic cholera. The 

 lower animals do not have malaria, yellow fever, scarlet fever, 

 or measles. The negro, as a race, is more immune to yellow 

 fever than the white race. 



Acquired immunity is that resistance which is acquired by 

 having a disease, by being vaccinated, or by injections with 

 antiserums. That immunity which is acquired by having the 

 disease, or by vaccination, is called active, and that acquired 

 by being inoculated with an antiserum, as, for example, an 

 antitoxin, is called passive immunity. Vaccination is the 



