28 BACTERIA. 



the above-named forms. The individuals may eventually swarm 

 out and continue their development in an isolated condition. 

 Such mucilaginous masses occur especially upon moist vegetables 

 (potatoes, etc.), on the surface of fluids with decaying raw or 

 cooked materials, etc. The mucilaginous envelope is thrown into 

 folds when the Bacteria, with their mucilaginous cell-walls, 

 multiply so rapidly that there is no more room on the surface of 

 the fluid. 



The cells of the Bacteria are constructed like other plant-cells 

 in so far as their diminutive size has allowed us to observe them. 

 The cell-wall only exceptionally shows the reactions of cellulose 

 (in Sarcina, Leuconostoc ; also in a Vinegar-bacterium, Bacterium 

 xylinum) ; a mucilaginous external layer is always present. The 

 body of the cell mostly appears to be an uniform or finely granu- 

 lated protoplasm. Very few species (e.g. Bacillus virens) contain 

 chlorophyll ; others are coloured red (purple sulphur Bacteria) ; 

 the majority are colourless. Bacillus amylobacter shows a reaction 

 of a starch-like material when treated with iodine before the 

 spore-formation. Some Bacteria contain sulphur (see p. 37). 

 The body, which has been described as a cell-nucleus, is still of a 

 doubtful nature. 



Artificial colourings with aniline dyes (especially methyl- violet, 

 gentian-violet, methylene-blue, fuchsin, Bismarck-brown and 

 Vesuvin) play an important part in the investigations of 

 Bacteria. 



MOVEMENT. Many Bacteria are self-motile; the long filaments of 

 Beggiatoa exhibit movements resembling those of Oscillaria. In 

 many motile forms the presence of cilia or flagella has been proved 

 by the use of stains ; many forms have one, others several cilia 

 attached at one or both ends (Fig. 23) or distributed irregularly 

 over the whole body ; the cilia are apparently elongations of the 

 mucilaginous covering and not, as in the other Alga3 of the proto- 

 plasm. In Spirochcete the movement is produced by the flexibility 

 of the cell itself. Generally speaking, the motion resembles that 

 of swarm- cells (i.e. rotation round the long axis and movement in 

 irregular paths) ; but either end has an equal power of proceeding 

 forwards. 



The swarming motion must not be confounded with the hopping motion of the 

 very minute particles under the microscope (Brownian movement). 



VEGETATIVE REPRODUCTION takes place by continued transverse 



