150 DIPHTHERIA AND PSEUDOD1PHTHERIA. 



Blood-serum from sheep or calves, 3 parts; 



Peptone-bouillon containing 1 per cent, of 



glucose, 1 part. 



Mix, distribute among test-tubes, sterilize, and harden by 

 exposing in a slanting position in a steam sterilizer at 97 

 C. for two hours. It should have a slightly alkaline reaction 

 to litmus. 



On this mixture at 37 C. after twelve hours the colonies 

 are round, grayish- white, about the size of a pin-head ; 

 later they become larger, elevated, and yellowish, with the 

 centre more opaque than the periphery. At the end of a 

 few days the colonies have a diameter of from 3 to 5 milli- 

 meters. 



In bouillon at 37 C. the cultures present small clots 

 deposited on the side and at the bottom of the tube. Some 

 of the culture floats on the surface of the liquid, forming a 

 thin whitish pellicle. The bouillon, which is at first cloudy, 

 becomes in a few days clear, and remains so. The sugars con- 

 tained in the bouillon are fermented, and it is due to their 

 fermentation that this medium has at first a tendency to be 

 acid ; but subsequently, when the fermentation is complete, 

 become decidedly more alkaline. On gelatin the colonies 

 develop very slowly. They appear white, round, irregu- 

 larly notched, and somewhat granular, never attaining a large 

 size. On agar the growth presents the same characteristics 

 as on blood-serum ; but on the surface of agar plates the 

 colonies are quite characteristic, having a dark elevated centre 

 and flat periphery, with a radiated appearance and indented 

 edges. On potato the growth is invisible at first ; and at 

 the end of several days a thin whitish veil seems to cover the 

 portion of the potato which has been inoculated. In milk it 

 grows at a temperature as low as 20 C., without any appre- 

 ciable change of the medium. 



Pathogenesis. Diphtheria, along with tetanus, should be 

 classified among the toxic diseases. As a matter of fact, the 

 symptoms met with in cases of diphtheria are due to the 

 effects of the toxins secreted by the bacilli; very few, if any, 



