B. DIPHTHERIA ON SERUM-MIXTURE. 245 



having decayed teeth, the morphology of which is so 

 like that of the bacillus of diphtheria that they might 

 easily be mistaken for that organism if subjected to 

 microscopic examination alone. 



The bacillus diphtheria of Loffler (its discoverer) can 

 readily be identified by its cultural peculiarities in con- 

 nection with its pathogenic activity when introduced 

 into tissues of susceptible animals. In guinea-pigs and 

 kittens the results of its growth are identical with those 

 found in the bodies of human beings who have died of 

 diphtheria. 



When studied in pure culture, its morphological and 

 cultural peculiarities are as follows: 



In morphology it varies greatly in size and shape, 

 averaging 2.5 to 3 / in length and 0.5 to 0.8 p in thick- 

 ness. Its morphological characters are so peculiar as te 

 render its detection on cover-slip preparations, and in 

 sections from diphtheritic membranes, in most cases an 

 easy matter. Sometimes appearing as a regular straight 

 or slightly bent rod, with rounded ends, it is especially 

 characteristic to find irregular, bizarre forms, such as rods 

 with one or both ends swollen, and very frequently rods 

 broken at irregular intervals into short, sharply marked 

 segments, either round, oval, or with straight sides. 

 Some forms stain uniformly, others in various irregular 

 ways, the most common being the appearance of deeply 

 stained granules in a lightly stained bacillus. 



GROWTH ON SERUM-MIXTURE. The medium upon 

 which it grows most rapidly and luxuriantly, and which 

 is best adapted for determining its presence in diphthe- 

 ritic exudations is, as has been stated, the blood-serum 

 mixture of L5ffler. (See chapter on Media.) On the 

 blood-serum mixture the colonies of the bacillus diph- 



