CLASSIFICATION OF BACTERIA 
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G. CLASSIFICATION OF BACTERIA. 
Relation to Higher Plants.— The position of bacteria in the Plant 
Kingdom is indicated in the following table: 
Plant Kingdom 
Cryptogamia 
Thallophyta 
1 
Phanerogamia 
Algaj 
1 
Schizomycetes 
Bacteriacese 
1 
Fungi Lichens 
1 1 
Saccharomycetes Hyphomycetes 
Blastomycetes (molds) 
(yeasts) 
ubacteriaceae 
Coccacese 
Bacillacese 
Spirillacese 
Treponemata 
Chlamydobacteriacese 
Streptothrix 
Phragmidothrix 
Crenothrix 
Cladothrix 
Actinomyeetes 
A complete natural classification of bacteria based upon purely 
morphological criteria is impossible at the present time. The monot- 
ony of form observed in this group of organisms merely suffices to 
classify them into three great divisions: Cocci, Bacilli and Spirilla. 
Further subdivision into groups which are potentially families, genera 
and species is accomplished by arranging them according to their 
physiological, chemical, pathological and serological characteristics. 
Even this artificial procedure is unsatisfactory, for bacteriological 
diagnosis is a subject which has developed under the stress of practical 
needs, and as bacteria play a part in many fields of activity, it has 
inevitably followed that the criteria whereby they are recogni'zed 
vary greatly according to the art or science in which they are contem- 
plated. Even the same species may be identified by wholly different 
characteristics. Notwithstanding the difficulties which surround the 
grouping of bacteria, Migula^ has worked out a system of classification 
based upon purely morphological characteristics, which effect at least 
a primary separation of bacteria into smaller subdivisions; this is 
moderately satisfactory so far as it goes, and it is the one commonly 
adopted.^ 
With certain additions it is as follows: 
The True Bacteria: Eubacteriace^. 
1. Cocacece. Cells in the free state spherical. 
(a) Micrococcus. Cells spherical. No definite sequence of planes of septation. 
(b) Diplococcus. Organisms habitually occur in pairs. 
(c) Streptococcus. Planes of septation parallel. Form longer or shorter chains. 
(d) Tetracoccus. Planes of septation alternate, and at right angles in two planes 
of space. Form groups of four or tetrads. 
1 System d. Bakterien, Jena, 1907. 
- This classification does not include the filterable viruses, the Rickettsia bodies or 
the Bacteriophage. 
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