46 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



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. 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 char- 

 acteristic 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 a 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, noting each characteristic and 

 comparing it with those described above. 



The beginner is. strongly recommended to procure a series 

 of slides of diphtheria bacilli from a bacteriological labora- 

 tory, and to study them carefully. 



Hoffmann's bacillus (Plate I., Fig. 2) is frequently met with 

 in throat cultures. It is about as long as the short form of 

 diphtheria bacillus, but decidedly plumper, and is more uniform 

 in shape and size. These bacilli stain deeply, sometimes 

 uniformly, but more often with an unstained septum across 

 the middle : banded forms are rare. They exhibit the same 

 arrangement, and are often grouped in pairs. Clubbed forms 

 do not occur. 



The diphtheria bacilli which occur in films made direct 

 from the swab are similar to those seen in cultures 

 but are often thicker; they may stain uniformly, and 

 clubbed forms are rare. It is unusual to be able to make an 

 absolute diagnosis as to their nature, but it may be done at 

 times. Yet such an examination is often useful. If sus- 

 picious bacilli are present you should inject antitoxin forth- 

 with; if no suspicious bacilli are seen it is safe to wait for the 

 result of the cultural examination. Here the use of Gram's 

 stain (which need not necessarily be associated with a counter- 

 stain) is most useful. If you are quite certain that your 

 material was taken from the affected area, and if you find no 

 stained bacilli in a fairly thick film, it is safe to withhold anti- 

 toxin pending developments, and vice versa. There are not 



