BACTERIACE.E : THE BACILLUS OF DIPHTHERIA 



287 



Loffler's blood serum is the medium of choice. The colonies 

 develop at 37 C. in 8 to 12 hours as grayish, slightly elevated 

 points and become 2 to 3 mm. in diameter in the course of 48 



A B 







t> x 



FIG. 118. Forms of B. diphtheria in cultures on Loffler's serum. A, Charac- 

 teristic clubbed and irregular shapes with irregular staining of the cell contents. 

 Xnoo. B, Irregular shapes with even staining. X 1000. (After Park and 



Williams.) 



hours. Contiguous colonies become confluent. On glycerin 

 agar after 24 hours at 37 C., the colony is coarsely granular 

 with a somewhat jagged outline. Many variations from this 



FIG. 119. Forms of B. diphtheria in cultures on agar. A, Bacilli^small and 

 uniform. Xiooo. B, Spherical forms in culture 24 hours old. On Loffler's serum 

 this same organism produced granular forms. X 1410. (After Park and Williams.) 



typical appearance occur. Growth in gelatin is slow and ceases 

 below 20 C. The medium is not liquefied. The bacillus grows 

 in milk without producing coagulation. In broth the growth 



