28 Comparative Studies 



lated was less than the minimum fatal dose, so that the 

 additional toxin generated by the diphtheria bacilli of low 

 virulence would be sufficient to kill the animal. Control 

 animals inoculated with like amounts of toxin remained 

 alive. He believes that it is not impossible to increase the 

 virulence of acid-producing bacilli, but that non-acid pro- 

 ducing pseudo-diphtheria bacilli cannot be made virulent. 

 He succeeded in making a non-virulent bacillus, derived 

 from a case of empyema following measles, virulent by 

 inoculating it along with diphtheria toxin. 



Prochaska (30) reports on sixteen cases in which the 

 pseudo-diphtheria bacilli were found. These cases were 

 found in making diagnoses of diphtheria, and were all 

 cases of throat infection. Thirteen of the cultures were 

 from cases of follicular angina. Another culture came 

 from a case of pharyngeal and nasal diphtheria. In this 

 case the typical L,6fner bacilli were also found. When 

 grown on blood serum they could not be differentiated from 

 Loffier bacilli by their size, and on microscopical examina- 

 tion resembled the pseudo-diphtheria bacilli. Inoculation 

 into animals gave negative results. The other two cultures 

 were isolated from the throats of children sick with scarlet 

 fever. In each of these cases there was a typical diphtheria 

 membrane in the throat, yet no virulent bacilli could be 

 found. 



M. Neisser (31) gives a method of staining for differ- 

 entiating between the diphtheria bacilli and pseudo- 

 diphtheria bacilli which he considers very reliable. The 

 solutions used are, first, one gramme powdered methylene 

 blue (Griibler) dissolved in 20 c. c. of 96 per cent alcohol ; 

 to this is added 950 c. c. of distilled water and 50 c. c. of 

 acetic acid; and, second, two grammes of vesuvin dis- 

 solved in a litre of boiled distilled water. Filtration, 

 especially of the latter solution, is necessary. Cover-slips 

 prepared in the usual manner are stained in the first solu- 

 tion for from one to three seconds, washed in water, and 



