240 BACILLUS DIPHTHERIA. 



Loeffler's blood-serum mixture, consisting of 3 parts of 

 blood-serum and 1 part of 1 per cent, glucose-bouillon, is 

 the most satisfactory culture-medium for the diphtheria bacil- 

 lus. This is the medium which is used for making bacterio- 

 logic examinations of material obtained from the throats of 

 persons suspected of having diphtheria. A growth is present 

 in five hours, although it is invisible. The colonies are 

 plainly to be seen nine hours after inoculation of the blood- 

 serum. They appear as pearly-gray or yellowish-gray, slightly 

 raised dots with irregular borders (Fig. 100), steadily increase 



FIG. 100. 



Colonies of diphtheria bacilli. X 200. (Park.) 



in size, and finally become confluent, forming a nodular yel- 

 lowish-gray growth. 



On agar-agar and glycerin-agar development occurs more 

 slowly unless the culture was transplanted from blood-serum, 

 when development takes place more rapidly. The colonies 

 are large, granular, and much darker in the centre than in 

 the periphery. The growth may be so luxuriant as to resem- 

 ble a colony of a staphylococcus. 



In gelatin stab cultures small whitish colonies form along 

 the line of inoculation, with a slight surface growth. The 

 gelatin is not liquefied. 



