12 CLASSIFICATION. 
Zopf, who insists upon the polymorphism of these low organisms, divides 
the bacteria into four groups: 
Genera, 
Streptococcus, 
1. Coccocrea# —Up to the pre- Merismopedia, 
sent time, only known in the form of Sarcina, 
cocci. Micrococcus, 
Alscococcus. 
2. BACTERIACE®.—Have for the ] Bacterium, 
most part spherical, rod-like, and | Spirillum, 
filamentous forms ; the first (cocci) , Vibrio, 
may be wanting; the last are not Leuconostoc, 
different at the two extremities; fila- Bacillus, 
ments straight or spiral. Clostridium. 
8. LEPTOTRICHES. — Spherical, . 
rod-shaped, and filamentous forms; ene 
the last show a difference between the ¢ pies midiothriz. 
two extremities ; filaments straight Te brie 
orspiral; sporeformation not known. D . 
4, CLADOTRICHE®. — Spherical, ) 
rod-shaped, filamentous, and spiral | 
forms ; the filamentous form pre- | Cladothriax. 
sents pseudo-branches ; spore forma- | 
tion not known. 1 
The main objection to this classification is that it assumes a pleomorph- 
ism for the bacteria of the second group—Bact-riaceae—which has only been 
established for a few species, and which appears not to be general among the 
rod shaped and spiral bacteria. 
De Bary divides the bacteria into two principal groups, one including 
those which form endospores, and the other those which are reproduced by 
arthrospores. But our knowledge is yet too imperfect to make this classifi- 
cation of value, and the same may be said of Hueppe’s recent attempt at 
classification, in which the mode of reproduction is a principal feature. 
The classification of Baumgarten (1590) appears to us to have 
more practical value, and, with sligit modifications, we shall adopt 
it in the present volume. This author divides the bacteria into two 
principal groups, as follows : 
Group I. Species relatively monomorphous. 
GrovupP IL. Species pleomorphous. 
The first group includes the micrococc?, the bacilli, and the 
spirilla; the second group the spirulina of Hueppe, leptotrichece 
(Zopf), and cladotrichee. 
The pleomorphous species described by Hauser under the generic 
name Proteus are included in the second group among the spirulina. 
In the present volume we have described these pleomorphous species 
among the bacilli. 
The Cocct, in the classification of Baumgarten, constitute a single 
genus with the following subgenera: 1, Diplococcus ; 2, Strepto- 
coccus ; 8, Merismopedia (Zopf)—‘‘ Merista” (Hueppe); 4, Sar- 
cina (Goodsir) ; 5, Micrococcus (‘‘ staphylococci”). 
The BacILui are included in a single genus embracing all of 
