DIPHTHERIA. 5! 



shaped like a stirrup, the flat bar being drawn along the 

 surface of the medium from bottom to top just as a rake 

 is drawn along a flower bed. 



Now examine your specimens in the way described 

 on page 34. 



CHARACTERS OF THE DIPHTHERIA BACILLUS. 



The following are the chief points which are con- 

 sidered 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 great assistance ; a 

 specimen 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. Their 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 



E 2 



