400 BACTERIOLOGY. 



makes its isolation by this method a matter of but little 

 difficulty. 



After twenty-four hours in the incubator the tubes 

 present a characteristic appearance. Their surfaces are 

 marked by more or less irregular patches of a white 

 or cream-colored growth, which is usually more dense 

 at the centre than at the 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 are 

 irregularly segmented. They are rarely or never regu- 

 lar 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 irregularity 

 in outline is the morphological characteristic of bacillus 

 diphtherice of Loffler. 



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, especially when they are stained only by the 

 usual method i. e., with Loffler's methylene-blue. 

 There are other organisms present in the mouth-cavity, 

 particularly in the mouths of persons having decayed 



