74 CLASSIFICATION OP THE BACTERIA 



further coalescence will undoubtedly result and that soon, we hope in pro- 

 portion 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 fermenta- 

 tion products ; 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 

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



