IQO BACTERIA 



in the body and in culture, which is intensely poisonous. See 

 chapter on bacterial products. 



Pathogenesis. Diphtheria in man means generally an infection 

 of the mucous membrane of the upper respiratory tract, with the 

 formation of false membranes. The latter may cause death by 

 suffocation. Infection may occur in the skin, vulva, or prepuce. 

 The toxin not only causes a local necrosis, with the formation of an 

 exudate, consisting of fibrin and leucocytes, but also grave systemic 

 action, with marked degeneration of important nerves and nerve 

 centers, and also of the parenchyma of the kidneys, liver, and heart, 

 paralysis following. In certain structures fragmentation of the 

 nuclei of the cells is noted. Guinea pigs, cats, horses, and cows, 

 may be infected artificially, but the disease never occurs spon 

 taneously in these animals. Horses, dogs, and cattle are susceptible 

 to its toxin. Diphtheria bacilli often have associated with them 

 streptococci, which add to their virulence, and complicate the 

 disease. Endocarditis, adenitis, pneumonia, abscesses, and empy- 

 emia, may be caused by them. There may be puerperal diphtheria, 

 due to the infection of the puerperal tract. Diphtheria is ^spread 

 mostly by personal contact with individuals suffering from the 

 disease, or with convalescents, in whose throats virulent bacilli 

 linger, perhaps, for months. It may originate from infected milk, 

 contaminated from human sources. 



Perhaps the most important source of infection, especially during 

 an epidemic, is the healthy bacillus carrier who, wholly unaware 

 of his condition, is carrying virulent germs in his throat. This 

 further indicates that individual resistance or susceptibility plays 

 an important part in infection. 



Immunity is natural, active, artificial, or passive. Active im- 

 munity, following infection, is generally a permanency, for, once 

 infected, the individual, if he recovers, may be considered immune 

 for a time, though some individuals are more susceptible, and suffer 

 several attacks. In active immunity anti-toxin is found in the blood, 

 and recovery, and subsequently, immunity is due to this- fact. Anti- 



