42 LABORATORY BACTERIOLOGY 



EXERCISE XIV 



THE CLASSIFICATION OF BACTERIA 



68. The term " bacteria " is a general and popular one used 

 to designate a large group of microscopic plants, the Schizo- 

 mycetes. These organisms, which are widely distributed in 

 nature, have been classified into a certain few families and 

 genera most of which have a large number of species. Many 

 of these species have been described, but there are many which 

 have not. In classifying the bacteria, the genera are based on 

 morphologic characters ; while, as a rule, the species are deter- 

 mined by means of their biochemic, physiologic, or. pathogenic 

 properties. Several systems of classification have been proposed, 

 but the one which seems to be the most^satisfactory is by Migula. 

 This classification utiUzes the morphology to such good advan- 

 tage that its adoption seems desirable. It requires, however, 

 some serious changes in the accustomed nomenclature. This, 

 however, is true of any logical system. The restoration of the 

 genus Bacterium, and the assigning to it of all non-motile, rod- 

 shaped organisms, changes the genus of some of our most 

 common pathogenic bacteria from Bacillus to Bacterium. The 

 most conspicuous of these are the Bacilli of tuberculosis, 

 glanders, and diphtheria, all of which are placed in Migula's 

 classification in the genus Bacterium. The families and genera 

 recognized by him are appended. 



FAMILIES 



I. Cells globose in a free state, not elon- qO 

 gating in any direction before divi- 

 sion into I, 2, or 3 planes . . .1. Coccaceae. — ^ 

 II . Cells cylindrical, longer or shorter, and 

 only dividing in i plane, and 

 elongating to twice the normal 

 length before the division. 



