326 SA GTEBIOLOQ Y. 



serum mixture than do other organisms, makes its iso- 

 lation 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 col- 

 onies 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 noticexl 

 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 reg- 

 ular in outline. If the preparation has been stained 

 with Lceffler'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 irregularity 

 in outline is the morphological characteristic of the 

 bacillus diphtherke of Ijoeffler. 



It must be remembered, however, that the diagnosis 

 of diphtheria should not under all circumstances 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 



