CHARACTERISTICS OF BACTERIA 45 



Reaction of media is of the greatest importance in causing variation 

 in the functions of bacteria, and is one which has until recently been 

 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 Neu- 

 mann call spore-bearing organisms bacilli, and nonspore-bearing ones 

 bacteria. 



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

 ing 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 anthracis, according 

 to Migula, and 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 arti- 

 ficial 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 bouillion cultures are preferable, and 

 the preparation should be made by applying a vaseline ring to the slide, 

 then putting a drop of the bouillion 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 away with 

 and the preparation keeps for hours. This is a convenient method for 

 agglutination tests. 



