26 



OUTLINES OF BACTEEIOLOGY 



--;.'-,^V 



smaller, until ultimately complete separation ensues. When stained 

 specimens of these stages are examined, in no case is it found that a 

 wall is thrown across as in the Bacteriaceae and Coccaceae. Instead, 



the walls on either side follow the 

 constriction (Fig. 40), and ultimately 

 meet. The walls of each daughter- 

 cell, at the separation-area, are 

 trimmed to conform to the shape 

 of the cell, and the only connection 

 between them is a thread of mucilage, 

 which, however, soon disappears, 

 leaving the two cells free. 



The process in this genus is abso- 

 lutely different in pryiciple from 

 any process of cell-division inside 

 the vegetable kingdom. It is, in 

 essentials, a division by fission, 

 similar to the process among the 

 lower organisms in the animal king- 

 dom. It differs, however, in the possession by these organisms of a 

 definite cell-membrane. 



4. Cell-division in the Thread-bacteria. Cell-division in the organ- 

 isms included under Chlamydobacteriaceae has not been accurately 

 studied. We have seen that there are two types of cell-division, one 

 in which the partition is initiated by the formation of a new cell- 

 wall across the cell (Bacteriaceae and Coccaceae), and one in which it 

 is initiated by a process of constriction (Spirillaceae). There can be 

 little doubt that in the various members of the Thread-bacteria the 

 method of cell-division follows one or other of these two types. In 

 Gallionella ferruginea and Leptothrix ochracea, although we do not 

 know all the details of cell-division, we known enough to be able to 

 state that it belongs, in essentials, to the method which obtains in 

 the Spirillaceae. We shall deal with these two species when we come 

 to the treatment of the Iron-bacteria. 



Fig. 40. — Stages in division of spiral cells. 

 (See text.) 



13. SPOEES. 



Vegetative reproduction, as seen above, is effected by cell-division 

 followed by growth of the daughter-cells, a method which enables 

 the bacteria to multiply very rapidly. The capacity of resistance of 



