1882.J 



MICKOSCOPICAL JOUKNAL. 



be. When the bacteria form a scum 

 upon the surface they form petalo- 

 coccus or petalo-bacteria. 



Davaine's classification, which is 

 convenient, is as follows : — 



Twisted. 



micro-, mesa- and mega-bacteria. 

 Then, according as there are one, two 

 or several cells united, he designates 

 them as mono-, diplo- and strepto- 

 coccus, or bacteria, as the case may 



Filaments straight, or bent, but not twisted 

 A. Moving spontaneously. B. Immovable. 



a. Rigid. b. Flexible. 



Bacterium. Vibrio. Bacteridium. Spirillum. 



Dr. Luerssen has proposed the following classification, which seems to be 

 excellent : — 



I. Cells not in filaments, separating immediately after division, or in couples, free 

 or united into colonies (Zoogloea) by a gelatinous substance. 



A. Cells dividing in one direction only. 



a, cells globular : Micrococcus. 



b, cells elliptical or shortly cylindrical : Bacterium. 



B. Cells dividing regularly in three directions, thus forming cubical families, having 

 the form of pockets strung crosswise, and consisting of 4, 8, 16, or more cells : Sarcina. 



II. Cells united into cylindrical filaments. 



A. Filaments straight, imperfectly segmented. 



a. filaments very fine and short, forming rods : Bacillus. 



b. filaments very fine and very long : Leptothrix. 



c. filaments thick and long : Beggiotia. 



B. Filaments wavy or spiral. 



a. Filaments short and stiff. 



a. filaments slightly wavy, often forming woolly flocks : Vibrio. 



b. filaments spiral, stiff, moving only forward or backward : Spirillum. 



b. Filaments long, flexible, with rapid undulations, spiral through their whole length, 

 and endowed with great mobility : Spirochaste. 



Billroth's classification is com- 

 mendable for its simplicity, but there 

 are facts to be mentioned further on 

 which tend to prove that some of the 

 different forms of bacteria are 

 distinct species. Nageli follows Bill- 

 roth to some extent. He finds that 

 forms, precisely alike in their appear- 

 ance under the microscope, occur 

 under very difiierent conditions, and 

 produce different effects. He there- 

 fore supposes that they have become 

 adapted to the different conditions in 

 which they are found, and recent ex- 

 periments afford no little support to 

 this idea. Cohn, supported by Pas- 

 teur, Koch and other competent 

 authorities, declares that there are 

 well-defined species of bacteria, 

 which are characterized by physiolo- 

 gical phenomena peculiar to them- 

 selves. 



Taking the evidence as it stands 

 now, as far as it is familiar to the 

 speaker, it seems clear that there are 



distinct species ; but any single spe- 

 cies may be found in such totally dif- 

 ferent forms, that the identity of the 

 forms cannot be determined without 

 a study of the growth and propaga- 

 tion of the particular specimens un- 

 der examination. Thus, Bacillus an- 

 thracis, in a certain stage of its 

 growth, produces spores which can- 

 not be distinguished by their ap- 

 pearance from micrococci. These 

 spores, however, do not multiply by 

 division like micrococci, and they 

 are not killed by a temperature which 

 is fatal to the latter. The necessity 

 of a knowledge of the life-history of 

 these forms in naming them is, from 

 this fact, apparent. 



In opposition to Cohn's views, the 

 experiments of Prof. Law may be 

 cited, which tend to prove that by 

 cultivation alone, a harmless species 

 can be made virulent, while an in- 

 fectious species can be made entirely 

 harmless. 



