BACTERIA AS PLANTS. 37 



tion of bacteria so complete as to characterize 

 the different species accurately. 



Even with our present incomplete knowledge 

 of what characterizes a species, it is necessary to 

 use some names. Bacteria are commonly given a 

 generic name based upon their microscopic ap- 

 pearance. There are only a few of these names. 

 Micrococcus, Streptococcus, Staphylococcus, Sarcina, 

 Bacterium, Bacillus, Spirillum, are all the names in 

 common use applying to the ordinary bacteria. 

 There are a few others less commonly used. To 

 this generic name a specific name is commonly 

 added, based upon some physiological character. 

 For example, Bacillus typhosus is the name given 

 to the bacillus which causes typhoid fever. Such 

 names are of great use when the species is a com- 

 mon and well-known one, but of doubtful value 

 for less-known species. It frequently happens 

 that a bacteriologist makes a study of the bac- 

 teria found in a certain locality, and obtains thus 

 a long list of species hitherto unknown. In these 

 cases it is common simply to number these spe- 

 cies rather than name them. This method is fre- 

 quently advisable, since the bacteriologist can 

 seldom hunt up all bacteriological literature with 

 sufficient accuracy to determine whether some 

 other bacteriologist may not have found the 

 same species in an entirely different locality. 

 One bacteriologist, for example, finds some sev- 

 enty different species of bacteria in different 

 cheeses. He studies them enough for his own 

 purposes, but not sufficiently to determine whether 

 some other person may not have found the same 

 species perhaps in milk or water. He therefore sim- 

 ply numbers them a method which conveys no 

 suggestion as to whether they may be new species 



