EXAMINATION OF LIVING BACTERIA. 31 



means of wliich. a specimen may be most quickly 

 classified ; whilst other systems, although perhaps 

 more scientifically correct, are much more difficult to 

 use, and on that account would not serve our present 

 purpose. 



As concerns the more minute structure of the bac- 

 terium cell, there is not much to be said; a differen- 

 tiation in its interior is only very rarely to, be observed, 

 even in the largest forms. Only so much is certain, 

 that all bacteria possess, in addition to their proto- 

 plasm, a membrane which, as it appears, is generally 

 of an albuminous constitution, but more rarely con- 

 sists of the same materials as that of ordinary plant 

 cells, namely cellulose. 



So far no nucleus has been demonstrated in bacteria, 

 but lately it has been considered that the whole con- 

 tents of the cell is composed of nuclear substance. 



