DIPHTHERIA BACILLUS 189 



Habitat. It has not been found in sewage, or sewer gas, soil 

 or water, the disease therefore is never transmitted by these means. 

 Has been found in the throat, nose, and in the conjunctivas of 

 healthy bodies. In disease, the organism is mostly found in the 

 throat, but has been isolated from all the organs in some fatal 

 cases. Sometimes it is discovered in the throats of animals. 

 Though its action is local, it elaborates a toxin which acts 

 systemically. 



Cultures. On gelatine plate the growth is scanty and raised. 

 This medium is never used for cultivating this organism. The gela- 

 tine is not liquefied. On glycerine agar plates the growth, though 

 moderate, is typically characteristic, but very slightly raised above 

 the medium, and is of duller lustre. Old colonies become yellowish- 

 brown, the center of which, under a magnification of sixty diameters, 

 appears darker, and with ravelled edges. On Loffler's blood 

 serum mixture, the organism grows rapidly and well. This and 

 ascites-glycerine-agar culture media are the best for it. Bouil- 

 lon made from fresh meat is an excellent medium for its growth. 

 The bouillon, which must be alkaline and freshly made, becomes 

 first cloudy; then a fine precipitate settles, and over the surface a 

 delicate pellicle forms. The reaction of the culture presents three 

 types: A, is acid in the beginning, and becomes progressively more 

 acid. B, is alkaline from the start, and progressively more alkaline; 

 this is the most toxic growth. C, acid at the start, becoming 

 alkaline finally. The growth is not so luxuriant as in B, nor is 

 there as much toxin produced. In milk, the growth is luxuriant, 

 without coagulation. The reaction is amphoteric, but in old cul- 

 tures it becomes alkaline. On potato, rendered alkaline, it will 

 grow, but not characteristically. 



Chemical Activities. No gas is formed, or any curdling or 

 gelatine dissolving ferments, but H 2 S, and indol, are produced. 

 Acids are evolved from sugars; even the sugar found in meat is 

 converted into lactic acid. In the manufacture of toxin, this muscle 

 sugar must -be removed. A soluble toxalbumin is created, both 



