52 BACTERIOLOGICAL DIAGNOSIS. 
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. 
Hoffman’s bacillus is dealt with subsequently. 
3. Theiv staining veactions——The diphtheria bacillus 
stains readily with all the stains in common use for 
bacteriological purposes. It usually (but not invariably) 
stains irvegulavly, deeply stained portions alternating 
with others which remain colourless. This gives rise to 
a beaded appearance, and forms sometimes occur which 
can hardly be distinguished from short chains of strep- 
tococci. When a powerful stain is applied for a long 
time this appearance may be lost. 
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. 
It stains by Gram’s method. A beginner should 
always test his results in this way. If suspicious bacilli 
do not retain the violet stain they are not those of 
diphtheria. 
4. Theiy avvangement.—This is a most characteristic 
feature, but it is one which is difficult to describe. The 
old comparison to the strokes which form a Chinese 
letter is a fairly good one; the bacilli lie in little groups, 
some lying parallel to one another, and some at various 
angles with these. The characteristic arrangement is 
best seen in a specimen made from a pure culture of 
the short form. 
Before coming to a conclusion as to the presence or 
absence of diphtheria bacilli from an examination of 4 
stained film, make a very thorough search; if no bacilli 
are seen make several more films and examine them. 
When you see a group of bacilli examine it carefully 
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