A textbook of bacteriology : including the etiology and prevention of infective diseases and a short account of yeasts and moulds, haematozoa, and psorosperms / Edgar M. Crookshank.

  • Crookshank, Edgar M. (Edgar March), 1858-1928.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: A textbook of bacteriology : including the etiology and prevention of infective diseases and a short account of yeasts and moulds, haematozoa, and psorosperms / Edgar M. Crookshank. Source: Wellcome Collection.

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    remains solid up to a temperature of about 45° C. It is there- fore substituted for gelatine in the preparation of a jelly for the cultivation of those bacteria which will only grow, or grow best, in the incubator at the temperature of the blood. It may also be employed at ordinary temperatures for bacteria which liquefy gelatine. The preparation is conducted on much the same principles as those already described. Instead, however, of 100 grammes of gelatine, only about 20 grammes of agar-agar are employed (1*5 to 2 per cent.), and to facilitate its solution it must be allowed to soak in salt water overnight. For the filtration, flannel is substituted for filter-paper, or may be used in combination with the latter. The hot-water apparatus is in variably employed, unless, to accelerate the process, the glass funnel and receiver are bodily transferred to the steam steriliser. If the conical cap cannot be replaced, cloths laid over the mouth of the steriliser must be em- ployed instead. It may be necessary to repeat the process of filtra- tion, but it must not be expected that such a brilliant transparency Fig. 34.—Incubator. can be obtained as with gelatine. The final result, when solid, should be colourless and clear; but if slightly milky, it may still be employed. A little liquid gradually collects in the tubes, being expressed by the contraction of the.agar-agar. Wort-gelatine is used in studying the bacteria of fermentation. It is made by adding from 5 to 10 per cent, of gelatine to beer-wort. Glycerine Agar-agar.—This is prepared by adding 5 per cent. of. glycerine to nutrient agar-agar, after the boiling and before the filtration, and other modifications can be made for special purposes by the addition of grape-sugar or of gelatine.