132 CONTAGION AND CONTAGIOUS DISEASES. 



their specific effects ; hence the importance of the destruction or 

 disinfection of these carriers of contac^ion. 



CLASSIFICATION OF MICROBES. 



There are various systems of classification, — namely, of Muller, 

 1773, who established two genera — monas and vibrios — and 

 grouped them with the Infusoria, but a scientific classification 

 was not made until Ehrenberg in 1838 described four genera, 

 namely : — 



I. Bacterium filamenti — straight, rigid. 

 11. Vibrio- „ — snake-like, flexible. 



III. Spirillum „ — spiral, rigid. 



IV. Spirochete „ — spiral, flexible. 



Dugardin in 1841 united spirillum and spirochete, and classed 

 them thus : — 



I. Bacterium filamenti — rigid, vacillating. 

 II. Vibrio- „ — flexible, undulatory. 



III. Spirillum „ — spiral, rotatory. 



And up to 1853 bacteria were considered as Infusoria; but 

 Eobin then pointed out their affinity to Leptothrix, and Davaine 

 in 1859 demonstrated that they were vegetables and allied to 

 the Algae, and his conclusions are now universally adopted. 



The classification of Cohn is now generally accepted, and he 

 considers that the bacteria are a distinct group belonging to the 

 Algre, and divisible into four tribes, including six genera. 



I. Sphserobacteria — globules (Micrococcii). 

 II. Microbacteria — short rods (Bacteria). 



If the length of a rod be less than twice its breadth, it is considered 

 a bacterium, if longer, a bacillus. 



III. Desmobacteria — long rod (Bacillus and Vibrio). 



IV. Spirobacteria — spirals (SpirochcUte and Spirillum). 



Cohn noted, notwithstanding the placing of them with the 

 Algffi, that the absence of chlorophyll connected the bacteria to 

 fungi ; and Na?geli subsequently adopted this view, and termed 

 them schizomycetes (cleft or fission fungi). 



A word or two may now be said about the action of microbes ; 



