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 fixed through the International Congress 

 of Zoologists and of Botanists respectively. Unfortunately, 

 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 accoimt 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 (1872-75) 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 

 recapitulate, cell wall, protoplasm, vacuoles, metachromatic 

 granules, capsules, flagella, spores, cell forms, and cell group- 

 ings. Most bacteria show not more than three or four of 

 these features, so that it is impossible by the aid of morphol- 

 ogy alone to distinguish from each other the large number 

 of different kinds which certainly exist. In the various 

 systems which are conceded to be the best these charac- 

 teristics do serve to classify them down to genera, leaving 

 the "species" to be determined from their physiological 



