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

  • Edwin O. Jordan
Date:
1931
Catalogue details

Licence: In copyright

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

    35/830 page 33
    asbestos pad only long enough to dissolve the gelatin; it should be stirred constantly. It is then cooled to 60 C., the reaction adjusted, and an egg, dissolved in 30 cc. of water, stirred slowly in. The medium is placed in a flask and cautiously heated in an autoclave to 10 pounds* pressure for five minutes in order to coagu¬ late the albumin. Filtration through a towel moistened with hot water should give a clear filtrate which can then be tubed and sterilized. Gelatin may be autoclaved for five minutes at 120 C. and still solidify if placed at once in the ice-box. In warm weather 12 per cent of gelatin is neces¬ sary. Special care should be taken to prepare gelatin each time in a uniform way, since otherwise the bacterial growth will vary considerably due to the differences in the media.1 The usual method of deter¬ mining the gelatin-liquefying properties of bacteria is to study stab- or plate-cultures in this medium incubated at 20 C. for one to six weeks. The appearance of stab cul¬ tures is sometimes quite dis¬ tinctive (see Fig. 102, p. 406). The progressive liquefaction of the medium should be noted at intervals. In the form of growth and the extent or shape of the liquefied zone, plate colonies sometimes contribute important infor¬ mation concerning the metabolism of the organisms, and may aid materially in their identification (Fig. 5). Rothberg2 has suggested that organisms which do not grow rapidly or at all at 20 C. may be grown in gelatin at 25 to 37 C. (according to their temperature relations) for eighteen to forty-eight hours, and then a portion of the culture inoculated on the surface of gelatin in a test-tube and incubated for fifteen days at 20 C. The production of gelatinases 1 Whipple: Tech. Quart, 1902, 15, p. 127. 2 Rothberg: Abstracts of Bact., 1917, 2, p. 12. See also Rush and Palmer: Jour, of Bact., 1921, 6, p. 571. Fig. 5.—Gelatin plate showing lique¬ fying and nonliquefying colonies (From “The Nature of the World and of Man,” (1926) Courtesy of the University of Chicago Press).
    digitised image 1
    digitised image 2
    digitised image 3