MYCOBACTERIACEiE: THE BACILLUS 6f DIPHTHERIA 305 



at 37° C. the broth is injected into two guinea-pigs in doses of 

 0.5 c.c. and one of the guinea-pigs should receive at the same time 

 diphtheria antitoxin. In this way virulent diphtheria bacilli 

 may be accurately detected. 



■ The very large number of examinations that have been made 

 by various boards of health have shown that the diphtheria 

 bacillus may persist in the throat for a long time —occasionally 

 several weeks after the patient has apparently recovered; also 

 that diphtheria bacilli are occasionally found in the throat, when 

 there is an inflammatory condition without any pseudo -membrane 

 and that they not only appear in an apparently healthy throat, 

 especially in hospital nurses and in children who have been asso- 

 ciated with cases of diphtheria, but also in those who have had 

 no traceable contact with diphtheria cases.^ It has been found 

 that bacilli sometimes occur in the throat, which have all the 

 morphological and cultural properties of the diphtheria bacillus, 

 but which are devoid of virulence when tested upon animals. 

 Such diphtheria bacilli have frequently been called pseudodiph- 

 theria bacilli. A baciUus closely resembling the diphtheria bacillus ^ 

 but without virulence, has been found in xerosis of the conjunctiva. 

 It is called the xerosis bacillus. If not a transformed diphtheria 

 bacillus, it is at least closely related. The diphtheria bacillus is 

 subject to wide variations in morphology, so that, in dealing with 

 unknown cultures where the forms are not characteristic and in- 

 jection into animals is without result, it may be dif&cult to decide 

 whether or not the organisms are diphtheria baciUi. 



The disease is undoubtedly transmitted very largely by 

 immediate contact, especially with persons harboring the bacilli 

 but not seriously ill, and by f omites. Children in school or at 

 play readily transfer secretions of the mouth, 'and a cough or 

 sneeze may distribute such material over a wide area. 



Immunity to diphtheria was produced by Von Behring in 



189P by injecting the toxin into animals, the general method of 



procedure being quite similar to that followed in the production 



1 ShoUy: Journ. Infect. Dis., Vol. IV, 1907, pp. 337-346- ■> 



20 



