§ I.] Structure of the Bacterium-cell. 7 



bacterium of sugar factories. On the other hand, Nencki found 

 that the membranes of certain putrefactive Bacteria not distinctly 

 determined are in a great measure composed, like the proto- 

 plasm which they enclose, of the mycoprotein mentioned on 

 page 4. Lastly, a statement of Neisser (65) must also be men- 

 tioned in this place ; he suspects, from the behaviour of the 

 membrane or envelope of the Bacterium of xerosis conjunctiva 

 in the presence of reagents, that it contains a considerable amount 

 of fatty matter. Further investigation into these points is at all 

 events desirable. The membranes of Cladothrix and Crenothrix 

 which live in water are often coloured brown by the introduc- 

 tion of compounds of iron. 



Many Bacteria are capable of free movement in fluids. They 

 rotate about their longitudinal axis, or they oscillate like a 

 pendulum and move rapidly forwards or backwards. Search 

 has consequently been made for organs of motion, and these 

 are supposed to have been found in certain very slender filiform 

 appendages, cilia or flagella, which are attached singly or in 

 pairs to the extremities of rod-shaped Bacteria. Such cilia are 

 present in many relatively large cells not belonging to the Bacteria, 

 and endowed like them with the power of free movement in fluids, 

 the swarm-cells, for example, and swarm-spores of many Algae 

 and some Fungi. In these cases the cilia oscillate rapidly as 

 long as the movement continues, causing rotation round the 

 longitudinal axis, and may consequently be considered to be 

 the active organs of motion. In the swarm-cells of the Algae 

 they are processes, projections as it were, from the surface of 

 the protoplasmic body, and belong therefore to the protoplasm. 

 When the protoplasm is surrounded by a membrane, the cilia 

 pass out through openings in the membrane. But no such 

 characteristic structural conditions have been observed in the 

 Bacteria. Delicate thread-like processes have certainly been 

 observed occasionally at the points above-mentioned in coloured 

 specimens which have been exposed to desiccation. That they 

 are really there and not, or at least not always, in the imagina- 



