i 9 2 INFECTION AND IMMUNITY 



There are evidently many different breeds of the 

 diphtheria bacillus, and its pathogenic virulence is 

 increased or diminished as a result of conditions re- 

 lating to its growth. A series of cases in very sus- 

 ceptible individuals is favourable to an increase in the 

 virulence of the germ. On the other hand, when 

 obtained from the throat of one who is comparatively 

 immune, or cultivated in artificial media outside of 

 the body, it is less virulent. 



While the most robust children are subject to 

 attack, delicate and poorly nourished children are 

 more susceptible and more likely to die. A chronic 

 or acute catarrhal inflammation of the throat or nasal 

 passages predisposes to infection. 



The bacillus of diphtheria was first described by 

 the German pathologist, Klebs, in 1883, and the fol- 

 lowing year the fact that it is the specific cause of 

 this disease was demonstrated by LofHer, a surgeon 

 in the German army and a pioneer in bacteriological 

 researches. Hence it is often spoken of as " the 

 Klebs-Loffler bacillus." Cultures of this bacillus 

 are very pathogenic for guinea-pigs, rabbits, chickens, 

 pigeons, and cats, and to a less extent for dogs, 

 horses, and cattle. Rats and mice have a natural 

 immunity. The immunity of certain individuals is 

 shown by the fact that when associated with diph- 

 theria patients they may carry virulent diphtheria 



