Manual of bacteriology / by Robert Muir and James Ritchie.

  • Muir, Robert, Sir, 1864-1959.
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: Manual of bacteriology / by Robert Muir and James Ritchie. Source: Wellcome Collection.

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    determined. The bacterial cell consists of a sharply con- toured mass of protoplasm which reacts to, especially basic, aniline dyes like the nucleus of an animal cell. From this fact it has been deduced that there is probably a close relationship between the protoplasm of bacteria and the chromatin of the nuclear protoplasm. To speak generally, a healthy bacterium when stained presents the appearance of a finely granular or almost homogeneous structure. The protoplasm of the bacterial cell is surrounded by an envelope which is probably of a gelatinous nature, and which can in some cases be demonstrated by overstaining a specimen with some of the aniline dyes, when it will appear as a halo round the bacterium. This envelope may sometimes be seen to be of considerable thickness. Its innermost layer is probably of a denser consistence, and sharply contours the contained protoplasm, giving the latter the appearance of being surrounded by a membrane. It is only, however, in some of the higher forms that a true membrane occurs. Sometimes the outer margin of the envelope is sharply defined, in which case the bacterium appears to have a distinct capsule, and is known as a capsulated bacterium {vide Fig. i. No. 4 ; and Fig. 50). The cohesion of bacteria into masses depends largely on the character of the envelope. If the latter is glutinous, then a large mass of the same species may occur formed of individual bacteria embedded in what appears to be a mass of jelly. When this occurs, it is known as a zoogloea mass. On the other hand, if the envelope has not this cohesive property the separation of individuals may easily take place, especially in a fluid medium in which they may float entirely free from one another. The bacterial envelope does not, as in the case of most vegetable cells, contain cellulose. Motility.—As has been stated, many bacteria are motile. Motility in a species is associated with the possession of wavy thread-like appendages called flagella, which for their demonstration require the application of special staining methods {vide Fig. i, No. 12; and Fig. 7 8). They have been shown to occur in many bacilli and spirilla, but only m two