244 BACTERIOLOGY. 



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 here and there by more or less irregular 

 patches of a dense 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 col- 

 onies may be seen, these large irregular patches are the 

 most conspicuous objects on the surface of the serum. 

 Now and then almost nothing else can be made out on 

 the tubes. 



The cover-slips made from the membrane at the 

 time the cultures were prepared will be found in 

 many cases to present a great variety of organisms, 

 but conspicuous among them will be noticed slightly 

 curved bacilli of very 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 reg- 

 ular in outline. If the preparation has been stained 

 with Loffler's alkaline methylene-blue solution many 

 of these irregular rods are seen to be marked by cir- 

 cumscribed points in their protoplasm which stain 

 very intensely ; they appear almost black. This ir- 

 regularity in outline is the morphological character- 

 istic of the bacillus diphtherias of Loffler. 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 mouth of those 



