110 A MANUAL OF BACTERIOLOGY 



oxygen, carbon, nitrogen, certain salts, and water. 

 Although some microbes are anaerobic, they require 

 oxygen, which is obtained from the carbohydrates 

 and albuminoids of the medium in which they live, 

 or from the free oxygen which may be dissolved in 

 that medium. 



Before considering the various classifications of 

 microbes, we mention the fact that microbes in 

 general are sometimes called Bacteria, but as there 

 is a genus of that name, it is better that the word 

 should be applied only when one is alluding to 

 microbes of that genus. The study of microbes 

 (which includes all forms of Schizomycetes) has been 

 consequently termed Bacteriology ; but it is an un- 

 fortunate name, which, at the present time, cannot 

 well be replaced by another. 



Microbes may be simply divided into aerobic 1 ' 

 and anaerobic 2 forms. Bacillus spinosus and Bacillus 

 cedematis maligni are examples of the former ; while 

 Micrococcus candicans and Bacillus sultilis are ex- 

 amples of the latter kind. 



Microbes may be also divided into pathogenic 

 (disease-producing), septic (putrefactive), zymogenic 

 (fermentive), and chromogenic (pigment-forming) 

 forms. 



The Schizomycetes, which Sachs includes in his 

 group the Thallophytes, have been classified by Cohn 3 

 into five genera : 



(1) Spherobacteria or micrococci. 



1 Those requiring free access of oxygen (air). 



2 Those which do not require free oxygen. 



3 Beitrdge zur Biologie der Pjlanzen, 1872 et seq. 



