THE DIPHTHERIA BACILLUS 389 



highly pleiomorphic bacilli, usually slender straight or slightly curved 

 rods with rounded and frequently swollen ends. The size and shape 

 of the individual organisms vary greatly even in the same culture; 

 they are not uniformly cylindrical as a rule, but have club-like thick- 

 enings at one or both ends, or they are swollen in the middle and more 

 or less pointed at the ends. Occasionally one end only is thickened, 

 giving rise to a long, somewhat wedge-shaped rod. The distinctive 

 morphology is best seen in eighteen- to twenty-four-hour growths on 

 Loffler's coagulated blood serum; organisms from growths on agar 

 are more uniform in appearance. Diphtheria bacilli observed directly 

 in diphtheritic membranes are also less pleiomorphic than those from 

 blood serum cultures. The organisms occur singly or in pairs, very 

 uncommonly in short chains. The size is very variable, ranging from 

 0.3 to 0.8 micron in diameter and from 1.5 to 6 microns in length. 

 The organism as ordinarily seen in diphtheritic membranes is about 

 0.6 micron in diameter and about 4 microns in length. Branched 

 forms are occasionally seen, particularly in the membrane which 

 forms on old plain broth cultures. 



The stainable substance of the organisms is not uniformly dis- 

 tributed, but occurs in somewhat irregular concentration, giving rise 

 to three rather distinct types of bacilli: the granular, the barred, and 

 the solid. 1 Metachromatic granules (Ernst-Babes granules) are also 

 present, and, according to Williams, the diphtheria bacillus reproduces 

 by fission at one of these granules. It was originally supposed that 

 the metachromatic granules were only found in virulent strains and 

 that the non-virulent strains had no granules. Neisser 2 invented a 

 stain which brings out these granules very sharply. 3 It is now known 

 that the granules are not necessarily related to virulence, conse- 

 quently the Neisser stain is rarely used. Diphtheria bacilli stain 

 well with the ordinary anilin dyes and very characteristically with 



1 Wesbrook, Wilson, and McDaniel, Jour. Boston Soc. Med. Sc., 1900, iv, 75; Trans. 

 Assn. Am. Phys., 1900. 



2 Ztschr. f. Hyg., 1897, xxiv, 443. 



3 The stain is prepared in the following manner: 



A. Methylene-blue (Griibler's) 1 gram 



Alcohol, 96 per cent. 20 c.c. 



Glacial acetic acid 50 c.c. 



Distilled water . . . . . . 950 c.c. 



B. Bismarck brown 1 gram 



Distilled water 500 c.c. 



The smear, fixed in the flame in the usual manner, is covered with solution A for three 

 to five seconds, washed in water, then covered with B for three to five seconds. After 

 thorough washing in water, the preparation is ready for microscopic examination. 

 The granules are stained blue, the bodies of the bacilli brown. 



