BACILLUS DIPHTHERIA 297 



the serum mixture than do other organisms, makes its 

 isolation by this method a matter of but little difficulty. 



After twenty-four hours in the incubator the tubes 

 will present a characteristic appearance. Their surfaces 

 will be marked at different points by more or less irreg- 

 ular patches of a white or cream-colored growth which 

 is usually more dense at the centre than at its irregular 

 periphery. 



Except now and then, when a few orange-colored 

 colonies may be seen, these large irregular patches are 

 the most conspicuous objects on the surface of the serum. 

 Occasionally, almost nothing else appears. 



The cover-slips made from the membrane at the time 

 the cultures were prepared will be found on microscopic 

 examination to present, in many cases, a great variety of 

 organisms, but conspicuous among them will be noticed 

 slightly curved bacilli of irregular size and outline. In 

 some cases they will be more or less clubbed at one or 

 both ends ; sometimes they appear spindle in shape, 

 again as curved wedges ; now and then they will be 

 seen irregularly segmented. They are rarely or never 

 regular in outline. If the preparation has been stained 

 with Loeffler's alkaline methylene-blue solution many of 

 these irregular rods are seen to be marked by circum- 

 scribed points in their protoplasm which stain very in- 

 tensely ; they appear almost black. This irregularity 

 in outline is the morphological characteristic of the 

 bacillus diphtherice of Lceffler. It must be remembered, 

 however, that the diagnosis of diphtheria cannot be 

 made from the examination of cover-slip preparations 

 alone, for there are other organisms present in the mouth 

 cavity, particularly in the mouths of persons having de- 

 cayed teeth, the morphology of which is so like that of 



