ORGANIZATION OF THE BACTERIA. 35 



motion, and the form of the bacteria, in order to 

 classify them ; but what has just been said shows 

 clearly that these transitory phenomena cannot be 

 taken for generic or specific characters. 



Structure. — It was for a long time believed that 

 the bacteria were constituted of amorphous masses 

 of protoplasm, or of solid rods. The researches of 

 Hoffmann have shown that they have a true cellu- 

 lar structure. We shall describe, then, succes- 

 sively, their membrane, the contents, and the cilia, 

 which may be considered as belonging to the pro- 

 toplasm. 



Cell-membrane. — The extreme minuteness of 

 the bacteria usually prevents a direct demonstra- 

 tion of the cell-membrane, and the existence of 

 this envelope has not, heretofore, be^en clearly 

 demonstrated except by indirect proofs ; chemical 

 reactions, for example. 



Thus Hoffmann verifies the existence of a cellu- 

 lar envelope when " the contents, which is a trans- 

 parent plasma, are partly coagulated, as sometimes 

 happens, or disappear, and are then replaced by 

 air which shows precisely the form of the normal 

 bacterian cell." Warming, also, has not been able 

 to see the membrane, " which only appears dis- 

 tinctly when a vacuole has formed just against the 

 periphery." 



On the other hand, the action of chemical agents 

 upon bacteria proves that they have an envelope 

 of cellulose, which is colored by tincture of iodine ; 



