The principles of bacteriology : a practical manual for students and physicians / by A.C. Abbott.

  • Abbott, A. C. (Alexander Creever), 1860-1935.
Date:
1896
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Licence: Public Domain Mark

Credit: The principles of bacteriology : a practical manual for students and physicians / by A.C. Abbott. Source: Wellcome Collection.

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    remainder of the milk pipetted into test-tubes, about 8 c.c. to each tube, and sterilized by the intermittent process, at the temperature of steam, for three successive days. The separation of the cream may be accelerated and rendered more complete by one sterilization of the milk in the cylinder before it is placed in the ice chest. The cream is best separated from the milk by the use of a cylindrical vessel with stopcock at the bottom, by means of which the milk, devoid of cream, may be drawn olF. A Chevalier creamometer with stopcock at the bottom serves the purpose very well. It should be covered while standing. Milk may be used as a culture medium without any addition to it, or, before sterilizing, a few drops of litmus tincture may be added, just enough to give it a pale blue color. By this means it may be seen that dif- ferent organisms bring about different reactions in the medium ; some producing alkalies which cause the blue color to be intensified, others producing acids which change it to red, while others bring about neither of these changes. Similarly litmus solution is often added to gelatin and agar-agar for the same purpose. Milk may also be employed as a solid culture medium by the addition to it of gelatin or agar-agar in the pro- portions given for the pi'eparation of the ordinary nutri- ent gelatin or agar-agar. It has, however, in this form the disadvantage of not being transparent, and can there- fore best be used for the study of tiiose organisms which grow upon the surface of the medium without causing liquefaction. Nutrient gelatin and agar-agar can also be prepared