484 SYSTEMATIC. 



The classification of Zopf will lead the investigator to work upon 

 the same lines, and by tracing the life-history of individual forms 

 in pure-cultivations either to extend the work of establishing 

 protean species or to restrict the doctrine of pleomorphism to a few 

 forms. For though the author prefers the classification proposed by 

 Zopf, he is not prepared to accept his views entirely for instance, 

 to regard the bacterium of rabbit septicaemia as a micrococcus. 



Any arrangement at present can only be considered provisional, 

 and therefore the most practical classification must be considered 

 the best. In fact, much more investigation is required before we 

 can arrive at a permanent and thoroughly scientific classification 

 of the known bacteria. Many bacteria have been described by 

 different observers as different species which are really identical. 

 Many micro-organisms have been described and named as new 

 species with very insufficient investigation. The determination of 

 species rests upon the accumulated evidence afforded by a thorough 

 knowledge of their life-history. The morphological appearances 

 under different conditions must be carefully studied, the presence 

 or absence of movement and of spore-formation, and when present 

 the exact character; the appearances of colonies and of test-tube 

 cultivations in different media and under different circumstances ; 

 the liquefaction and other changes in nutrient media ; the nature 

 of the chemical products, if any, and the effect on the living animal 

 of the bacterium itself and of its products, in varying doses, must 

 all be taken into account. We must also ascertain whether the 

 bacterium is an aerobe requiring the presence of oxygen, or an 

 anaerobe growing only in the absence of it, or .a facultative anaerobe 

 growing equally well with or without it ; and lastly, we must know 

 whether the bacterium is a parasite requiring a living host, or a 

 saprophyte existing on dead animal or vegetable matter, or a 

 facultative parasite capable both of growing in the living animal 

 and of leading a saprophytic existence. Several writers have 

 classified the bacteria which have been described hitherto by taking 

 some of these characters into account, and so preparing a list which 

 is convenient for the purpose of bacteriological diagnosis. A system 

 of this kind is of value in leading investigators to supply information 

 which is wanting in order to verify and amplify the information 

 upon which the classification is based, and to identify species which 

 have been described under different names. 



