BACTERIUM DIPHTHERIA 75 
EXERCISE XXV 
BACTERIUM DIPHTHERIA 
112. The bacterium of diphtheria is often called the Klebs- 
Loeffler bacillus. It is the specific cause of diphtheria in man; 
but it is not, so far as known, the cause of diphtheria in 
pigeons and poultry. It is found in the throats of people 
suffering with diphtheria, and often in the throats and noses 
of those who have been exposed to it. These are designated 
as “germ cases.” Ordinarily it is not found elsewhere in the 
body, although it is occasionally discovered in the internal 
organs and blood. It usually remains in the throat for some 
days after its lesions have disappeared. Its appearance in the 
throat lesions is made use of in diagnosing the disease. For this 
reason’it is especially important that its morphology, as well as 
its cultural characters, should be carefully determined. Although 
this organism grows on nearly all of the media commonly used, 
its development is more rapid and its growth more characteris- 
tic on Loeffler’s blood serum. The bacterium of diphtheria 
seems to be modified in its morphology in growing on different 
media more than any of the other pathogenic bacteria. Particu- 
lar attention should be given to its morphology and staining 
properties. 
113. Work for this exercise. Examine microscopically, in 
hanging-drop and stained cover-glass preparations, the bacteria 
from the glycerin agar and Loeffler’s blood-serum cultures. 
Stain with alkaline methylene blue and note especially the way~ 
the bacteria stain. The preparation should be stained for fully 
5 minutes and then decolorized for a few seconds in 95% 
alcohol. 
Stain a few preparations after Neisser’s method (the staining 
solutions will be furnished) and compare with the methylene- 
blue stain. 
