VARIATIONS IN VIRULENCE OF BACILLI. 345 



ing the bacilli at an abnormally high temperature, namely 

 39.5 C, and in a current of air. By this method the 

 virulence was so much diminished that the organisms be- 

 came practically innocuous. When the virulence was much 

 diminished, these observers found that it could be restored 

 if the bacilli were inoculated into animals along with a 

 culture of the streptococcus of erysipelas, inoculation of 

 the bacilli alone not being successful for this purpose. If, 

 however, the virulence had fallen very low, even the presence 

 of the streptococci was insufficient to restore it. As a rule, 

 the most virulent cultures are obtained from the gravest 

 cases of diphtheria, though to this rule there are exceptions. 

 It has been abundantly established that after the cure of 

 the disease, the bacilli may persist in the mouth for two or 

 three weeks, though they often quickly disappear. Roux 

 and Yersin found by making cultures at various stages 

 after the termination of the disease, that these bacilli in 

 the mouth gradually become attenuated. These observa- 

 tions are of importance in relation to the subject of the 

 pseudo- diphtheria bacillus. At present it would scarcely 

 be safe to make a definite statement as regards the 

 relation of virulence to the size of the bacilli. Perhaps 

 the majority of observers have found that the bacilli 

 of the larger form are usually more virulent than those 

 of the shorter form ; but this is not invariably the case, 

 as sometimes short forms are obtained which possess an 

 extremely virulent character. Both the long and the 

 short forms may become attenuated in the same way. 



The so-called Pseudo -diphtheria Bacillus. Loffler, in 

 1887, was the first to describe a bacillus having closely the 

 characters of the diphtheria bacillus, but differing from it 

 in its want of virulence. To this organism he gives the 

 name pseudo-diphtheria bacillus, and looked upor^ it as a 

 distinct species. Hofmann, in 1888, published an account 

 of his investigations on this subject. He obtained the 

 pseudo -diphtheria bacillus from the throat in healthy 

 conditions, and also in non- diphtheritic affections. His 

 conclusions with regard to the distinct character of this 



