DIPHTHERIA. 51 
shaped like a stirrup, the flat bar being drawn along the 
surface of the medium from bottom to top just as a rake 
is drawri 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 f shape (Plate I., figs. 1 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 
E2 
