476 SYSTEMATIC. 



the affinity of the Bacteria and Vibrios to Leptothrix ; and Davaine, 

 in 1859, insisted that the Vibrios were vegetables, and were in 

 fact allied to the Algae. 



Since that time a flood of light has poured in upon this subject 

 through the writings of Hoffmann, Pasteur, Cohn, Rabenhorst, 

 Hallier, Billroth, Warming, Nageli, Magnin, Marchand, Sternberg, 

 Van Tieghem, Koch, Fliigge, De Bary, Zopf, Buchner, Hueppe, 

 Marshall Hall, and many others who have studied the morphology, 

 life-history, and classification of bacteria. 



Of all these writers we are most indebted to Cohn, not only 

 on account of his researches, which extended over many years, but 

 also for his system of classification, which has since been almost 

 universally adopted. 



In his first classification, published in 1872, Cohn considered the 

 Bacteria as a distinct group belonging to the Algse, and divisible 

 into four tribes, including six genera : 



I. Sphserobacteria . . globules (Micrococcus). 



II. Microbacteria . . short rods (Bacterium). 



III. Desmobacteria . . long rods (Bacillus and Yibrio). 



IV. Spirobacteria . . spirals (Sphirochaeta and Spirillum). 



Cohn noted, in spite of placing them with the Algse, that the 

 absence of chlorophyll connected the Bacteria to Fungi, and we find 

 Naegeli subsequently adopting this view, and employing the term 

 Schizomycetes or Fission-fungi. 



Billroth, in 1874, disputed the division into species, and con- 

 sidered that all the forms described by Cohn were but developmental 

 forms of one micro-organism, Coccobacteria septica. In the following 

 year Cohn answered the criticism of Billroth, and produced a second 

 classification, in which he still maintained that distinct genera and 

 species existed. Cohn considered the genera to be distinguished by 

 definite differences in shape, which were adhered to throughout life, 

 while some special feature, as a difference in size or physiological 

 action, or some minute difference in form, determined the various 

 species. 



The second classification of Cohn (1875) only differed from the 

 first in that, instead of keeping the bacteria as a separate group, he 

 placed them, from their close relationship with the Phycochromacae, 

 under a new group, the Schizophytes, and added the genera Lepto- 

 thrix, Beggiatoa, Crenothrix, Sarcina, Ascococcus, Streptococcus, 

 Myconostoc, and Streptothrix. 



Fliigge retained the term Schizomycetes, and divided them thus : 



