38 STUDY AND IDENTIFICATION OF BACTERIA. 



almost entirely neglected. In describing an organism at the present 

 time it is always necessary to note the reaction of the media, the tem- 

 perature at which cultivation took place and the age of the culture 

 when examined. 



In the following keys the term bacterium has been used as a general 

 designation for all schizomycetes. Migula calls motile rod-shaped 

 organisms bacilli, and nonmotile ones bacteria. Lehmann and 

 Neumann call spore-bearing organisms bacilli, and nonspore-bearing 

 ones bacteria. 



The B. typhosus is very motile and does not possess spores. Ac- 

 cording to Migula, it would be the Bacillus typhosus; according to 

 Lehmann and Neumann, the Bacterium typhosum. The B. anthracis 

 has spores and is nonmotile. Hence it would be Bacterium anthra- 

 cis, according to Migula, and the Bacillus anthracis, according to 

 Lehmann and Neumann. 



In the use of the keys at the head of each group of organisms it will 

 be observed that the primary separation is on the basis of morphology 

 the cocci in one group, the bacilli in three subgroups: one for those 

 rod-shaped organisms showing branching and curving forms, one for 

 the spore bearers and one for the simple rods. The spirilla are 

 grouped by themselves. 



An important method of differentiation is the reaction to Gram's 

 stain. It should be remembered that organisms carried along on 

 artificial media often lose their Gram staining characteristics; hence it 

 is desirable to determine this staining reaction in cultures freshly 

 isolated. Be sure that the stains, especially the aniline gentian violet 

 and the iodine solution, have not deteriorated. There is no more 

 important stain than this, and none which requires greater experience. 

 The chief causes of conflicting results are (i) working with old cultures 

 and (2) not having satisfactory staining solutions. 



Motility, as stated above, is at times difficult to determine. For this 

 purpose young eighteen-hour-old bouillon cultures are preferable, and 

 the preparation should be made by applying a vaselin ring to the 

 slide, then putting a drop of the bouillon culture in the center of the 

 ring (or a drop of water inoculated from an agar slant growth), then 

 putting on a cover-glass. By this method current movement is done 



