18 



BACTERIOLOGY. 



isochromatic dry plates, and more recently special methods have 

 been introduced, by Lbffler and others, by which they can be stained 

 and photographed with comparative facility. 



It is not certain whether the flagella are extensions of the cell- 

 wall, or derived from the internal protoplasm. Van Tieghem holds 

 the first view, and does not regard them as motile organs at all. 

 Zopf, on the other hand, adheres to the second view, and moreover 

 believes that they can be retracted within the cell-wall. 



Reproduction. — Bacteria multiply by fission and by processes 

 which may be considered as representing fructification. The 



"'O ^o '^^ 



Tig. 5.— Clostridium butykicum, x 1020. 



B. Stages of spore-formation. 



C. Stages of germination. 



; [After Prazmowski.] 



bacteria exhibiting the latter processes have been divided into two 

 groups, distinguished by the formation of endospores in the one and 

 of arthrospores in the other. In the process of fission the cell first 

 increases in size, and a transverse septum forms from the cell-wall, 

 dividing the internal protoplasm into two equal parts ; these may 

 separate and lead an independent existence, or remain linked 

 together. In chains of cocci the individual cells are easily visible 

 and distinct, but in the thread-forms resulting from the Knking 

 together of rods, as in the anthrax bacillus, the composition of the 

 thread is only demonstrated by the action of reagents. 



Endospore formation may be conveniently studied in Bacillus 

 anthracis, Bacillus megatherium, or Bacillus subtilis. The proto- 



