CORYNEBACTERIUM DIPHTHERIA. 393 



and, when magnified a little more highly, distinct single 

 rods are seen to project at the edge. The center is opaque 

 yellowish-brown (59, n a and 6). In still older cultures 

 dark irregular spots occur, the colonies become yet more 

 crumbly, the periphery more torn, and the inner part 

 more opaque (59, in). Colonies occur, however, espe- 

 cially upon better nutrient media (ascites-glycerin-agar), 

 which are rounder, thicker, and therefore more opaque 

 from the first, and finely granular (59, vi a and 6). After 

 a longer time such luxuriant colonies resemble perfectly 

 those of cocci or sarcinse (59, vn). Also all the other 

 forms reproduced in Plate 59 may occur as they are found 

 in closely related non-pathogenic forms. 



Glycerin-agar Streak. The same may be said of it as 

 of the growth upon glycerin-agar plates. There occur also 

 here more luxuriant and more delicate forms (58, i and 

 n). Especially upon glycerin-ascites-agar the cultures 

 are sometimes so luxuriant that they resemble those of the 

 Bact. coli or micrococci. (Compare 58, in and iv. ) In 

 many cases after two to six weeks the agar shows a brown 

 discoloration. 



Blood-agar Streak. Very good growth. 



In raw hens' eggs there is abundant growth, and upon cooked 

 white of egg there is a relatively luxuriant growth. 



Serum Culture. Loifler's coagulated blood-serum 

 mixture is often employed for cultures. It consists of the 

 serum of calves or sheep (or slightly alkalinized serum of 

 cows) to which is added one- third its volume l of neutral 

 veal bouillon (containing 1% peptone, 1% grape-sugar, 

 and 0.5% sodium chlorid). We find this nutrient medium 

 to possess about the same advantages as glycerin-ascites- 

 agar. 



Bouillon. After twenty hours a cloud is deposited, 

 either in the form of fine, dust-like granules upon the 

 sides and bottom of the tube, or (and what most authors 

 give as most frequent, but Escherich only seldom found 

 in Gratz) fine flocculi form, which are easily precipitated, 

 and, upon shaking, rise again. Both types are connected 



1 Escherich recommends one-fourth or one-fifth in order to insure 

 certain solidification of the serum upon heating. 



