CHAPTER IV. 



CLASSIFICATION OF BACTERIA AND THE IDENTIFICATION 

 OF SPECIES. 



Classification. Bacteria are classified into families and 

 genera by means of their morphology. The species are deter- 

 mined by their physiologic, biochemic or pathogenic proper- 

 ties. 



A number of methods or systems have been followed by 

 different writers in their classifications. As the form and 

 method of reproduction are the most constant features in 

 the morphology of bacteria they have been used as the basis 

 of most of the classifications. There are, however, a num- 

 ber of elements in the morphology, such as the production 

 of spores and the presence of flagella, that have been used 

 more or less for that purpose. As an illustration of the lat- 

 ter we have Messea's classification of bacteria which is based 

 on the presence and distribution of the flagella on the bodies 

 of the organisms. As illustrations of the earlier classifica- 

 tion, those of Cohn 1 , Ehrenberg 2 , Zoph 3 , De Bary 4 and Baum- 

 garten 5 may be mentioned. Cohn divided bacteria into four 

 genera or classes, represented by the following genera : Mi- 

 crococcus, Bacterium, Bacillus and Vibrio, Spirillum and Spir- 

 ochaeta. Ehrenberg placed all bacteria in four genera, 

 namely: Bacterium, Vibrio, Spirillum and Spirochaete. Du- 

 jardin 6 placed all bacteria in three genera : Bacterium, 

 Vibrio, and Spirillum. 



Beitr. f. Biol. der Pflanzen, Pt. I and II, 1882. 



2 Ehrenberg. Die Infusionstierchen als vollkommene Organis- 

 men, 1838. - 



3 Zoph, Zur Morphologie der Spaltpflanzen, Leipzig, 1882. 



4 De Bary. Vergleichende Morphologie und Biologic der Pilze, 

 Mycetozoen und Bacterien (1884) ; Vorlesunger iiber Bacterien, II 

 Aufl. (1887). 



5 Baumgarten. Lehrbuch der pathologischen Mykologie, 1890. 



6 Dujardin. loc. cit. 



