Morphology 419 



joined; usually the individuals are separate from one an- 

 other. The bacillus is peculiar in its pleomorphism, for 

 among the well-formed individuals which abound in fresh 

 cultures a large number of peculiar organisms are to be 

 found, much larger than normal, some with one end en- 

 larged and club shaped, some greatly elongated, with both 

 ends similarly and irregularly expanded. These bizarre 



Fig. 123. Wesbrook's types of Bacillus diphtheriae: a, c, d, Granular 

 types; a 1 , c 1 , d 1 , barred types; a 2 , c 2 , d 2 , solid types. X 1500. 



forms probably represent an involution form of the organ- 

 ism, for, while present in perfectly fresh cultures, they 

 are much more abundant in old cultures where scarcely a 

 single well-formed bacillus can be found. Distinct polar 

 granules can be denned at the ends of the bacilli. Occa- 

 sional branched forms are observed, and the diphtheria 

 bacillus probably belongs to the higher bacteria, though 

 Abbott and Gildersleeve* do not regard branching as a phase 

 of the normal development of the organism, do not find it 

 common upon the standard culture media, and so do not 

 think that it is properly classified elsewhere than among the 

 bacilli. 



No flagella have been demonstrated upon the bacillus, 

 and it is non-motile. It is almost purely aerobic. 



The involution of the diphtheria bacillus seems to occur 

 in proportion to the rapidity of its growth. Upon Lofrler's 

 serum mixture, which seems best adapted for its cultivation, 



*"Centralbl. f. Bakt. ; " etc., Dec. 18, 1903, Bd. xxxv, No. 3. 



