. Bacteriology and the public health. Bacteriology; Public health. F. 456 APPENDIX * "single stain" may be shortly mentioned. It is as follows. A clean cover-glass or slide is taken (cleaned with nitric acid and alcohol, or bichromate of potash and alcohol), and a drop of distilled water placed upon it. This is inoculated with a particle of a colony on the end of a platinum needle, and a scum is produced. The film is now " fixed " by slowly drying it over a flame. When it is thus dried, a drop of the selected stain ( gentian- violet) is placed over the film and allowed
. Bacteriology and the public health. Bacteriology; Public health. F. 456 APPENDIX * "single stain" may be shortly mentioned. It is as follows. A clean cover-glass or slide is taken (cleaned with nitric acid and alcohol, or bichromate of potash and alcohol), and a drop of distilled water placed upon it. This is inoculated with a particle of a colony on the end of a platinum needle, and a scum is produced. The film is now " fixed " by slowly drying it over a flame. When it is thus dried, a drop of the selected stain ( gentian- violet) is placed over the film and allowed to remain for a few seconds. It is then washed off with clean water, and the speci- men dried, and mounted in Canada balsam. The organisms will now appear under the micro- scope as violet in colour, and fig. stage for Fixing Films. will thus be more clearly seen than when unstained. " Double staining" is adopted when it is necessary to stain the organisms one colour and the tissue in which they are situated a contrast colour. The chief methods will be mentioned subsequently. 4. Sub-culture of Colonies.—The plate method was introduced by Koch in order to facilitate isolation of species. In a flask it is impossible to isolate individual species, but when the growth is spread over a comparatively large area, such as a plate, it is possible to obtain separate detached colonies, and this being done, the colonies may be replanted, by means of a platinum wire, in fresh media ; that is to say, a sub-culture may be made, each organism cultivated on its favourable medium and its manner of life closely watched. For example, a water may contain six species of bacteria. On the plate these six species would reveal themselves by their own peculiar growth. Each would then be isolated and placed in a separate tube, on a favourable medium, and at a suitable temperature. Thus each would be a pure culture ; , one, and only one, species would be present in each of the six
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