CHAPTER X. 

 THE RECOGNITION OF BACTERIA. 



THE most difficult thing in bacteriology is to be able 

 to recognize the bacteria which come under observation. 



A certain few micro-organisms are so characteristic in 

 shape and grouping as to be separated by a microscopic 

 examination. Some, as the tubercle bacillus, are charac- 

 teristic in their reaction to the anilin dyes, and can be 

 differentiated at once by this peculiarity. Some, as the 

 Bacillus mycoides, are so characteristic in their agar-agar 

 growth as to eliminate others. The red color of Bacillus 

 prodigiosus and the blue of Bacillus janthinus will speak 

 almost positively for them. The potato culture of the 

 Bacillus mesentericus fuscus and its close relative the vul- 

 gatus is quite sufficient to enable us to pronounce upon 

 them. Unfortunately, however, there are several hun- 

 dreds of described species which lack any one distinct 

 character that may be used for differential purposes, and 

 require that for their diagnosis we shall wellnigh ex- 

 haust the bacteriological technique in an almost fruitless 

 effort to recognize them. 



A series of useful tables has been compiled by Eisen- 

 berg, and is now almost indispensable to the worker. 

 Unfortunately, in tabulating bacteria we constantly meet 

 species described so insufficiently as to make them worse 

 than useless on account of the confusion caused. 



The only way to recognize a species is to study it 

 thoroughly and compare it, step by step, with the descrip- 

 tions and tables of known species compiled by Eisenberg 

 and others. 



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