30 BACTERIOLOGY. 



fluid like blood. The organic matter dries out on the cover- 

 glass first, whereas the bacterial cell dries later. In the 

 process of drying it naturally shrinks somewhat in size, 

 and hence a clear zone results between the dried organic 

 matter and the retracted dried cell. On staining the speci- 

 men a colorless zone will surround each cell and may there- 

 fore be easily mistaken for a capsule (Fig. 5 c). The 

 capsule, unlike the real membrane, does not stain easily 

 with anilin dyes. 



In certain organisms related to the bacteria, as the 

 beggiatoa, a hardening rather than softening of the mem- 

 brane takes place. This gives rise to a sheath or tube 

 which surrounds the individual elements and may be consid- 

 ered as analogous to the cell-wall of higher plants. Such 

 sheaths, however, are not met with among the true bacteria. 



The contents of the bacterial cell. The relatively hard and 

 more or less impenetrable cell-wall encloses the soft proto- 

 plasm which is the living portion of the cell. In it, there- 

 fore, are carried on the chemical and physical changes 

 necessary to life. It contains, like all protoplasm, a rela- 

 tively large amount of water. The solid constituents of the 

 protoplasm are chiefly nitrogenous, that is to say protein, 

 in character. Moreover, fatty substances are always pres- 

 ent, and in some species, as the tubercle bacillus, they may 

 make up a large percentage (30-40 per cent.) of the total 

 solids. There is reason to believe that at times a carbohy- 

 drate, like granulose, is present. The inorganic constitu- 

 ents, or ash, constitute, about 10 per cent, of the dried 

 cells. 



The composition of the bacterial cell will vary accord- 

 ing to the soil on which it grows. Moreover, it is undoubt- 

 edly influenced by the age of the individual cell. In view 

 of the different products elaborated by various species of 

 bacteria, it is evident that their chemical composition must 

 necessarily vary. 



