DIPHTHERIA 45 



CHARACTERS OF THE DIPHTHERIA BACILLUS 



The following are the chief points which are considered in 

 deciding whether a given stained slide does or does not show 

 the diphtheria bacillus. 



1. The shape of the bacillus is very variable, and this is a 

 feature which often affords us g'reat assistance ; a pure culture 

 in which all the bacilli present resemble each other exactly in 

 shape and size is not from a case of diphtheria. Diphtheria 

 bacilli are narrow rods; they are either straight or slightly 

 curved in an arc of a large circle or into an / shape (Plate I., 

 Figs, i and 2). Their ends are usually rounded, but it is not 

 uncommon to find forms with one end or both sharply pointed. 

 Lastly, clubbed forms are to be met with in almost all cultures, 

 though they are most frequent in those which have been 

 incubated for several days; they may be compared to a note 

 of exclamation ( ! ). 



2. Size. Two well-marked varieties occur. The long form 

 is about as long as a tubercle bacillus (to compare it with an 

 organism with which the practitioner may readily become 

 acquainted), or somewhat longer; it is decidedly thicker. The 

 short form is only about half as long and thick in proportion. 



We do not know anything as to the difference in 

 pathogenicity (if any) of the long and the short varieties of 

 the diphtheria bacillus. They appear to " breed true " for long 

 periods^ and cases of diphtheria caused by the one appear to 

 have as high a mortality as those caused by the other. 



Hoffmann's bacillus is dealt with subsequently. 



3. Staining Reactions. The diphtheria bacillus stains 

 readily with all the stains in common use for bacteriological 

 purposes. It usually (but not invariably) stains irregularly, 

 deeply stained portions alternating with others which remain 

 colourless. This gives rise to a septate, banded, or beaded 

 appearance, and forms sometimes occur which can hardly be 

 distinguished from short chains of streptococci. When a 

 powerful stain is applied for a long time this appearance may 

 be lost, and it is often absent in very short bacilli. 



The diphtheria bacillus stains deeply with thionin. This 

 often affords a certain amount of help in the diagnosis, as 

 many other bacilli do not stain nearly so deeply in the same 

 time. 



