CLASSIFICATION 51 



and consequently at a time when the isolation of organisms in pure 

 culture was a matter of extreme difficulty and uncertainty. One of the 

 first facts noted by the student in taking up bacteriology is the diffi- 

 culty in determining motility; this property should always be tested 

 on young cultures in bouillon. In Brownian movement there is a sort 

 of scintillating movement, but the bacterium does not move from that 

 part of the field. In current movement all the bacteria swarm in the 

 same direction, going very fast at times, and then more slowly. If in 

 great doubt, the mounting of the organisms in a 2 % solution of carbolic 

 acid will stop movement if it be true functional motility, while Brownian 

 and current movement are not interfered with. In true motility bac- 

 teria move in opposite and in all directions, and move away from the 

 place where first observed unless degenerated or dead. 



At times we judge of motility by the presence of this characteristic 

 in a few of the organisms seen in the microscopic field, the vast majority 

 of the bacteria not showing motility. A source of error can be present 

 when the bacteria are emulsified in a drop of water which might contain 

 motile bacteria. 



Reaction of media is a factor 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 temperature 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. According to Migula, 

 it would be the Bacillus typhosus; according to Lehmann and Neumann, the Bac- 

 terium 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 branch- 

 ing 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- 



