260 BACTERIOLOGY. 



A study of the above table will show that it makes 

 changes in the genus of some of the most common 

 bacteria, as in the restoration of the old genus bacte- 

 rium and the assigning to it of all non-motile, rod- 

 shaped organisms, thus altering the genus of some of 

 the most common pathogenic bacteria from bacillus to 

 bacterium. Other changes are seen in the spirilla. 

 Any such scheme is at times very arbitrary in placing 

 some varieties under one generic division and others 

 closely allied in another. It has also the objection, 

 already noted, that it is only one of several classifi- 

 cations already in use, and until some authoritative 

 body agrees on some one it is almost useless in such 

 a volume as this to change the usually employed names 

 for others which are, perhaps, intrinsically somewhat 

 better. Another important reason for waiting is that 

 with the increase of our knowledge we are constantly 

 changing the position of different bacteria. Thus such a 

 well-known germ as the tubercle bacillus is now found 

 to produce, under certain conditions, long thread-like 

 branching forms, so that it ceases to be under the clas- 

 sification of Migula a bacterium. We will, therefore, 

 simply use the usual nomenclature, and consider to- 

 gether, in so far as is practicable, certain groups of 

 bacteria whose members are closely allied to each other 

 in some one or more important directions. 



The Permanence of Bacterial Species. When we come 

 to study special varieties or groups of bacteria, such as 

 the bacilli which produce typhoid fever, diphtheria, and 

 tuberculosis, it is of great importance for us to deter- 

 mine, if possible, to what extent the peculiar character- 

 istics which each of these groups of bacteria possess are 

 permanent in the generations which develop from them. 



