10 BACTERIOLOGY. 



4-7. Spirillum undula treated by the method of drying, and 

 staining with aniline dyes ; in the different stages of division 

 and in different individuals the cell contents (Biitschli's "central 

 body " or " nucleus ") contract in various ways : 6 alone shows 

 a sort of division into two new central bodies that accords with 

 Biitschli's interpretation. In all the figures the cell substance is 

 dark, the cell wall, which is left free by the contraction of the 

 contents, is clearer and is faintly stained in the process of stain-- 

 ing the flagella ; the outer Jayer, however, is not a mantle oi 

 cytoplasm as supposed by Biitschli. 



be conceived to exist, and in this connection it 

 is safe to claim only that it is the lowest cell 

 form that can without question be regarded 

 as a plant. 1 Since we know certain unicell- 

 ular organisms whose relations to the plant 

 and animal kingdoms are doubtful, bacteria 

 are probably not the most rudimentary form 

 of cell. 



In the early studies of bacterial forms certain 

 kinds with marked characteristics were found in 

 connection with various specific diseases and 

 specific decompositions. These could be distin- 

 guished from one another with such ease that 

 particular stress was laid upon the description 

 of such typical, "regulation " forms. It came 

 to, be recognized later, however, that these dif- 

 ferent cell-forms are linked together by all pos- 

 sible intermediate stages. In order to permit 

 of a rapid orientation it has, therefore, become 

 the general practice to enumerate only three 

 chief form groups : 



1 Perty and F. Cohn were the first to recognize the affinity of these 

 organisms to the plant kingdom. 



