BACILLUS DIPHTHERIA 75 



As was pointed out by Abbott and is seen in 

 Fig. 73, the bacillus on blood serum grows out into 

 extremely long filamentous forms (6 p in length), 

 which, together with other features, has caused this 

 organism to be ranked by some observers with the 

 Streptotrichae. 



Variations in the culture material cause variations 

 in the morphology of the bacillus, but there appear 

 to be also well-marked varieties occurring in the 

 false membranes, which show differences both in 

 form and virulence, and whose differential characters 

 remain constant in successive cultures on the same 

 nutrient materials. Among virulent bacilli are well- 

 recognised long and short varieties. 



The effect of nutrient material on morphology is 

 shown in Fig. 74, which represents a culture on 

 gelatine of the same virulent organism as that seen 

 in Fig. 71. The bacillus is much shorter and stains 

 with much greater regularity, while the " clubbing," 

 though still present, is much less marked. 



Diphtheria can be produced by the inoculation of 

 the bacillus or its toxic products, and by various 

 methods animals can be protected or vaccinated 

 against either the organism or its poisons. The 

 blood serum of these protected animals is found to 

 be itself capable of securing the protection of other 



