CHAPTER XXXV. 



CLASSIFICATION AND DESCRIPTION OF SPECIES. 



In reviewing the history of the various classifications which have 

 from time to time been proposed, we shall see that the gradual 

 improvements in the means of studying such minute objects, 

 the methods of cultivating them artificially, and of studying their 

 chemistry and physiology, and the ever-increasing revelations of the 

 microscope, have resulted in establishing these microscopic objects as 

 members of the vegetable kingdom, ranking among the lowest forms 

 of fungi, but with regard to the division into genera and species we 

 are still in a position of doubt and uncertainty. 



Muller, in 1773, was the first to suggest a classification. He 

 established two genera, Monas and Vibrio, and grouped them with 

 the Infusoria. In 1824 Bory de Saint Vincent also attempted 

 a classification ; but it was not until Ehrenberg in 1838, and 

 Dujardin in 1841, worked at the subject, that a scientific distinction 

 of species was attempted. 



Ehrenberg described four genera : — 



I. Bacterium . . filaments straight, rigid. 



II. Vibrio . filaments snake-like, flexible. 



III. Spirillum . filaments spiral, rigid. 



IV. Spirochaeta . . filaments spiral, flexible. 



Dujardin united Spirillum and Spirochseta, and classed them 

 thus : — 



I. Bacterium . filaments rigid, vacillating. 



II. Vibrio . . filaments flexible, undulatory. 



III. Spirillum . . filaments spiral, rotatory. 



Bacteria were still considered as Infusoria, but in 1852 Perty 

 maintained that some of the smallest living organisms belonged to 

 the animal and others to the vegetable kingdom, and that Vibrios 

 without question belonged to the latter. In 1853 Robin pointed out 



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