A text-book of general bacteriology / by Edwin O. Jordan.

  • Edwin O. Jordan
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of general bacteriology / by Edwin O. Jordan. Source: Wellcome Collection.

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    about 37°. Lack of food is apparently not an adequate stimulus to spore-formation. In all cases a period of uninterrupted vege¬ tative multiplication precedes the appearance of spores, and the conditions necessary for the production of spores seem to arrive simultaneously for most of the cells in a culture. In at least some cases the cause of spore-formation is to be found in an accumulation of metabolic products in the culture; these may perhaps be acids, perhaps other injurious compounds.* It must not be forgotten that although some bacteria do not form spores under the con¬ ditions in which they are observed, it does not follow that they may not form spores under other and more suitable conditions. It is not possible to imitate with precision the “ natural” conditions of life for all micro-organisms, and there is no complete justification for the assumption that because an organism has never been ob¬ served to form spores it never does so. Physiologically the spore is to be considered as a resting-stage. It serves to tide the species over a period of dryness, famine, or unsuitable temperature, and to preserve alive in a hostile environ¬ ment a sufficient number of individuals until such time as favorable conditions recur. The spore stage is, in fact, physiologically anal¬ ogous to the periods of hibernation or estivation among higher forms of life. In this resting state the living matter of the spore may remain dormant for years or even for decades. (B) The Morphology of Masses of Cells In the case of many species of bacteria a single cell, when planted in a favorable medium and allowed to develop under suitable con¬ ditions of moisture, temperature, and air-supply, will in a few hours or days develop a “ colony” so large that it can be plainly seen by the naked eye. In some instances such masses of cells, especially when the growth occurs upon certain culture-media, possess salient peculiarities which are highly characteristic of the species. In others the differences between colonies of closely allied species are exceedingly subtle, and can be detected at times only by a trained eye. Growths upon the nutrient gelatin commonly used as a culture-medium are especially characteristic; on this * Migula: “System der Bakterien,” Jena, 1897, I, p. 177.
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