18 



tion forms of the plague bacillus are seen after twenty-four hours 

 Generally the greater number, or all, of the organisms from such a 

 growth present themselves as large spherical bodies, looking very 

 much like yeast cells ; later, large swollen club or dumbbell shaped, 

 spermatozoa-like or irregular forms make their appearance. The 

 most typical, and the most constant form on a 3.5 to 4 per cent 

 salt agar, after twenty-four to forty-eight hours, is the yeast-like, 

 large, spherical plague organism. There is no micro-organism 

 which forms this type so promptly and so regularly on salt agar 

 and which might be confounded with the plague bacillus. Hence 

 it is advisable in a first suspected plague case at the autopsy to 

 inoculate besides gelatin plates also ordinary agar tubes, bouillon 

 flasks, and salt agar tubes or plates. In bouillon flasks the bacilli, 

 at temperatures between 30° and 35° C, after twenty-four hours, 

 show a finely flocculent whitish, slowly increasing sediment. During 

 the next twenty-four hours the flocculi extend upwards from the 

 bottom along the walls. A fine whitish ring of growth then forms 

 on the surface and in course of time covers it. If the flask, is 

 protected from any motion and kept perfectly undisturbed, bands 

 and strands of bacilli finally grow downward from the surface 

 membrane. The contents of the flask now present an appearance 

 which somewhat reminds one of stalactite and stalagmite formation 

 A slight jar sends the stalactites to the bottom and destroys the 

 characteristic appearance. The stalactite formation can be assisted 

 by floating on the surface of the bouillon a few drops of an indifi erent 

 substance, such as butter, olive or cocoanut oil, small pieces of 

 cork, splinters of wood, etc. Of course, these. bodies should be 

 added to the bouillon before sterilization. The bouillon used in 

 connection with our plague w^ork has been one of a flxed degree of 

 alkalinity recommended particularly by Kossel and Overbeck as 

 most favorable for the development of the plague bacillus. Such 

 a bouillon is prepared in the ordinary manner and alkali is added 

 until the broth is neutral to litmus, then 0.5 gram of crystallized 

 soda is added to each 1,000 cubic centimeters. In bouillon cultures 

 the plague organism has a marked tendency to form longer chains, 

 which are composed of ten to twelve or even more small, short 

 bacilli. Such chains on first sight appear much like streptococci, 

 but a more careful examination reveals their proper structure. The 

 individual links of the chain are not arranged in a perfectly 

 straight line, but angles and bends are frequently seen. 



