9 
36 MORPHOLOGY OF THE BACTERIA. 
is not destroyed by caustic potash, ammonia, or 
even acids; and resists putrefaction for an ex- 
ceedingly long time. In this respect, it resem- 
bles the membrane of cellulose of vegetable cells 
(Cohn). 
We should add that Cohn claims to have suc- 
ceeded with high powers in seeing directly the 
cell-membrane. On the other hand, Warming has 
never succeeded in so doing. The last observer 
remarks also that the resistence of bacteria to 
acids, to alkalis, etc., does not seem to prove the 
existence of a membrane, “inasmuch as this may 
be the result of a particular condition of the 
plasma, which in all the bacteria is of a more con- 
sistent nature than in other plants.” 
Finally, the membrane may be, in certain bac- 
teria, tender, flexible and susceptible of move- 
ments of torsion. In others, it is rigid and 
incapable of bending. Cohn thinks also that it 
may swell and dissolve into mucilage, a fact which 
would explain the origin of this substance in the 
Zooglea. 
Protoplasm.— The contents of the cell is a 
nitrogenous substance, generally colorless, more 
highly refractive than water. 
In the smallest species, this protoplasm appears 
homogeneous; but in the bacteria of medium size, 
and above all in the large species, the contents of 
the cell encloses portions more highly refractive, 
vacuoles, special granules, and sometimes diverse 
coloring matters. — 
