CHAPTER V. 

 CLASSIFICATION. 



The arrangement of living organisms in groups accord- 

 ing to their resemblances and the adoption of fixed names 

 is of the greatest advantage in their scientific study. For 

 animal forms and for the higher plants this classification is 

 gradually becoming standardized through the International 

 Congress of Zoologists and of Botanists respectively. Un- 

 fortunately, the naming of the bacteria has not as yet been 

 taken up by the latter body, though announced as one of 

 the subjects for the Congress of 1916 (postponed on account 

 of the war). Hence there is at present no system which 

 can be regarded as either fixed or official. 



Since Miiller's first classification of "animalcules" in 1786 

 numerous attempts have been made to solve the problem. 

 Only those beginning with Ferdinand Cohn (1872-1875) are 

 of any real value. As long as bacteria are regarded as 

 plants, it appears that the logical method is to follow the 

 well-established botanical principles in any system for nam- 

 ing them. Botanists depend on morphological features 

 almost entirely in making their distinctions. The preceding 

 chapters have shown that the minute plants which are 

 discussed have very few such features. They are, to recapitu- 

 late, cell wall, 'protoplasm, vacuoles, metacliromatic granules, 

 capsules, flag ella, spores, cell forms and cell groupings. Most 

 bacteria show not more than three or four of these features, 

 so that it is impossible by the aid of morphology alone to 

 distinguish from each other the large number of different 

 kinds which certainly exist. Physiological activities must 

 be used as an aid to identification. Of the many systems 

 that have been proposed the only one that will be considered 

 in this work is : — 

 (44) 



