Elements of bacteriology for practitioners and students : with especial reference to practical methods / by S.L. Schenk ; translated from the German (by the author's permission) with an appendix / by W.R. Dawson.

  • Schenk, Samuel Leopold, 1840-1902.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: Elements of bacteriology for practitioners and students : with especial reference to practical methods / by S.L. Schenk ; translated from the German (by the author's permission) with an appendix / by W.R. Dawson. Source: Wellcome Collection.

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    the pores would he clogged hy solidification of the gelatine. To avoid using the hot-water funnel, Kirchner suggests allowing the gelatine to cool slowly in the steam steriliser, after turning out the flame; it is then after a few hours perfectly clear and can be filtered with facility. Instead of the folded paper, a thin layer of cotton- or glass-wool may be used for filtering. If a sample of the filtrate is taken in a test-tube and heated until it boils, it must remain clear and should also not become cloudy while cooling. Any turbidity, if such occurs, may possibly be due to the gelatine having been rendered too strongly alkaline in neutralising; as in heating such a solution the carbonic acid is driven off, and then compounds are thrown dowm which cause the turbidity. It need hardly be said that care must be taken in such cases to neutralise exactly in order to get an efficient gelatine. That perhaps other faults, such as inferior paper, dirty vessels, &c., may be to blame, is also evident, and such must be avoided in the preparation of nutrient media. Cloudiness is most easily dealt with by adding the white of a hen’s egg to the lukewarm gelatine while it is still fluid, and shaking so as to divide it finely, after which the solution is again boiled and filtered in the hot-water filter. Indeed it is the rule to add the white of an egg to nutrient gelatine immediately after neutralising, so as to ensure the avoidance of all faults of turbidity. The gelatine when ready should be clear and of an amber-yellow colour, and should not become cloudy on heating. Carefully cleaned test-tubes are filled with about 10 cubic centimetres each and plugged with cotton wool, or Schill’s double test-glasses may be used (see p. IG). The should be about eighteen inches square, and folding is begun by doubling it down the centre. The creased paper is finally gathered up, inserted into the funnel, and the superflous part cut off.]—Tn.