DIPHTHERIA BACILLUS 211 



pigs, cats, horses, and cows, may be infected artificially, but the 

 disease never occurs spontaneously 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 empyemia, 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 dur- 

 ing an epidemic, is the healthy bacillus carrier who, wholly una- 

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

 This further indicates that individual resistance or susceptibility 

 plays an important part in infection. (See Schick Test.) 



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

 munity, following infection, is seldom permanent for although the 

 individual, if he recovers, may be considered immune for a time, 

 some individuals are more susceptible, and suffer several attacks. 

 In active immunity anti-toxin is found in the blood, and recovery, 

 and subsequently, immunity are due to this fact. Anti-toxin 

 may be discovered in the blood, by mixing it with toxin of known 

 strength, and injecting it into guinea pigs. If these survive a 

 large lethal dose of the toxin, it is safely presumed that anti-toxin 

 was present in the serum abstracted. 



Passive artificial immunity is induced by injecting anti-toxin in 

 the bodies of persons exposed to diphtheria. It is most effective 

 but is short-lived, lasting only a few weeks. Serum therapy (see 

 anti- toxin in previous chapter). If there is one natural specific 

 cure for any disease, it is diphtheritic anti- toxic serum, which is 

 prepared by immunizing horses with toxin, and abstracting their 

 blood. The earlier it is given, the better are the chances of recov- 



