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. Their 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 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. Their arrangement. 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 d 

 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 



