PNEUMONIA AND DIPHTHERIA. 233 



known kinds of bacteria this appearance is only to be 

 seen in the Bacillus megaterium. Bat from this the 

 diphtheria bacillus can be very easily distinguished, 

 both by its form, and by the fact, that it never lique- 

 fies the gelatine, whereas the Bacillus megaterium 

 gradually does so. In gelatine puncture cultivations a 

 growth appears, which is similar to that of the Strep- 

 tococcus erysipelatos ; a great number of small round 

 whitish colonies develop along the track of the needle ; 

 on blood serum there forms a somewhat thick whitish 

 coating which is quite opaque, at any rate in the 

 middle. But the most characteristic of all is the cul- 

 ture in bouillon. Here small solid granules of a whitish 

 colour are formed, which either sink to the bottom, or 

 fasten themselves upon the sides of the vessel. As a 

 rule the bouillon does not become at all turbid, but 

 .occasionally a slight cloudiness occurs. 



The diphtheria bacillus is to be found chiefly in the 

 diphtheritic membrane, especially in the older portions ; 

 it has however been found in healthy men. It may be 

 that it resembles the Praakel's diplococcus in this, but 

 it is also possible that, in these isolated cases, some of 

 the organisms present in the mouth cavity, which are 

 very similar to the diphtheria bacillus, may have been 

 mistaken for it. 



