26 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



biityricus fluorescens liquefaciens immoMlis. The author 

 was indicating that he was dealing with a rod-shaped organ- 

 ism which fermented sucrose hy the formation of hutyric 

 acid, produced a fluorescent pigment in artificial media, 

 liquefied gelatin, and was nonmotile. It is quite as unnec- 

 essary to use complex names of this type as it is to have 

 the Christian name applied to an individual necessarily 

 descriptive of that individual. 



Many microorganisms have received common names. 

 These should not be confused with the true scientific names 

 even though they somewhat resemble them, for example, 

 the organism which causes epidemic pneumonia is termed 

 the pneumococcus. Its true scientific name is Diplococcus 

 pneumoniae. 



Many of the genera of bacteria belonging to the two 

 orders to be studied are not of sufficient economic import- 

 ance to warrant discussion in this connection. Only genera 

 which contain species that bring about noteworthy changes 

 are included in the discussion. 



First there is presented an artificial key for the diiJeren- 

 tiation of the economic genera. This is followed by the 

 classification of genera and families recommended by the 

 Committee on Nomenclature of the Society of American 

 Bacteriologists. 



It will be noted in the key and in the description of 

 genera and other groups that it is sometimes necessary to 

 use physiological rather than morphological criteria for 

 differentiation. For example, Gram's staining method 

 (discussed in a later chapter) results , in coloring some 

 organisms and leaving other organisms unstained. Some 

 organisms can produce acid or acid and gas from cer- 

 tain carbohydrates, other forms cannot. This fact is of 

 great value in separating related groups. Occasionally 

 the type of growth upon culture media may be of im- 

 portance. 



