EXERCISE XIV. 



THE CLASSIFICATION OF BACTERIA. 



62. Explanatory note. Bacteria is a general and pop- 

 ular term used to designate a large group of microscopic 

 plants, the Schizomycetes. 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 determined 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 

 utilizes the morphology to such good advantage that its 

 adoption seems desirable. It requires, however, some serious 

 changes in the accustomed nomenclature. 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 Bac- 

 terium. 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 fam- 

 ilies and genera recognized by him are appended. 



FAMILIES. 



I. Cells globose in a free state, not elongat- 

 ing in any direction before division 



into i, 2 or 3 planes i. Coccaceae. 



II. Cells cylindrical, longer or shorter, and 

 only dividing in one plane, and 

 elongating to twice the normal length 

 before the division. 



(i) Cells straight, rod-shaped, without 

 sheath, non-motile, or motile by means 

 of flagella 2. Bacteriaceae. 



