94 CLASSIFICATION OF THE BACTERIA. 



and thread bacteria. Nevertheless it was exceedingly convenient, 

 as it was based on some well-marked primary characteristics. If 

 the fission-fungus in question excited any form of disease in men 

 or animals, it was referred to the pathogenic group ; if it possessed 

 the faculty of producing colours, it was relegated to the category 

 of chromogenic bacteria ; and if it exhibited a capacity for effect- 

 ing those chemical changes which were comprised in the term 

 "fermentation" ( i), it was considered as zymogenic. A strict 

 adherence to this method of partition is impracticable, because 

 there are some bacteria which, on account of their range of 

 activity, would have to be placed in two, or even all three of 

 these classes. A large number of examples could be adduced in 

 support of this assertion ; it will be sufficient to cite merely a 

 single one, viz., Staphylococcns pyogenes aureus, the cause of 

 osteomyelitis (bone caries) and therefore pathogenic. However, 

 since it also, as its name implies, produces a golden-yellow colour- 

 ing matter, it is also chromogenic ; and, finally, from its power of 

 setting up lactic fermentation in suitable nutrient media, it is 

 therefore also zymogenic. 



From this example it will be evident that the domains of 

 Pathological and Technical Mycology cannot be rigidly kept sepa- 

 rate. On the contrary, their further coalescence will undoubtedly 

 result and that soon, we hope in proportion as fermentation 

 physiologists acquire a greater insight into the chemical changes 

 effected by bacteria, and pathologists determine the precise action 

 the bacteria exert on the organs of animals and plants. A fine, 

 but unfortunately still very isolated, example of the successful 

 combination of these two fields of research is afforded by the 

 labours of L. NENCKI (I.) on the bacterium which is the cause both 

 of " blown " cheeses and of inflammation of the udder in the cow. 



The distinction between chromogenic and zymogenic bacteria 

 can also be further maintained, not because there is any essential 

 reason for it, but because there are certain species of Schizomycetes 

 which are interesting to the technicist solely because they produce 

 colouring matters. 



So far as the zymogenic bacteria, in the narrower sense of the 

 term are concerned, i.e. those either cultivated, or dreaded, on 

 account of the chemical changes they produce, there is the same 

 need for a well-established consistent classification as in the two 

 groups just noticed. The changes effected by them are expressed 

 in terms having reference to the predominant fermentation pro- 

 ducts ; hence it is we speak of the bacteria of lactic fermentation, 

 acetic fermentation, and so on. This purely practical method of 

 classification will be adopted in the description about to be given. 

 Before passing thereto it will, however, be necessary to consider 

 the methods practised in the examination of these organisms, this 

 knowledge being essential for the study of the organisms them- 

 selves. This will form the subject of the two following chapters. 



