ORGANIZATION OF THE BACTERIA. 85 
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, been 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 ; 
