34 THE STORY OF GERM LIFE. 



rather by their physiological than their morpho- 

 logical characters. This is an unsatisfactory 

 basis of classification, and has produced much 

 confusion in the attempts to classify bacteria. 

 The problem of determining the species of bac- 

 teria is to-day a very difficult one, and with 

 our best methods is still unsatisfactorily solved. 

 A few species of marked character are well 

 known, and their powers of action so well under- 

 stood that they can be readily recognised ; but 

 of the great host of bacteria studied, the large 

 majority have been so slightly experimented upon 

 that their characters are not known, and it is im- 

 possible, therefore, to distinguish many of them 

 apart. We find that each bacteriologist working 

 in any special line commonly keeps a list of the 

 bacteria which he finds, with such data in re- 

 gard to them as he has collected. Such a list is 

 of value to him, but commonly of little value to 

 other bacteriologists from the insufficiency of the 

 data. Thus it happens that a large part of the 

 different species of bacteria described in literature 

 to-day have been found and studied by one in- 

 vestigator alone. By him they have been de- 

 scribed and perhaps named. Quite likely the 

 same species may have been found by two or 

 three other bacteriologists, but owing to the 

 difficulty of comparing results and the incom- 

 pleteness of the descriptions the identity of the 

 species is not discovered, and they are probably 

 described again under different names. The 

 same process may be repeated over and over 

 again, until the same species of bacterium will 

 come to be known by several different names, as 

 it has been studied by different observers. 



