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 tins respect, it resem- 

 bles the membrane of cellulose of vegetable cells 

 (Colin). 



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 resistance 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 

 Zooglcea. 



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. 



