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.

    43/830 page 41
    which a definite amount of culture may be run into the bottom of the tube. The neck is then drawn out in the flame and sealed off. Heating should be done with the bulbs completely immersed in a water-bath and held suspended by a wire away from the bottom frame. It is advisable to begin by exposing to a temperature of 50 C. for five minutes and then for ten minutes, repeating for every two degrees up to 70. Spores require still higher temperatures for their destruction. After being cooled quickly the bulb contents are emptied into a Petri dish and melted agar added, to determine by the development of colonies the number of live organisms present. Eijkman1 has called attention to an important error in such experi¬ ments. Many cells are so damaged by exposure to heat (and prob¬ ably the same is true of other disinfecting agents) that they develop exceedingly slowly, although their vitality is not destroyed. In one experiment with Bacterium coli no colonies were visible on a gelatin plate within three days after incubation of the heated culture, but on the same plate after fifteen days 670,000 colo- Fig. 9—Sternberg’s bulb for i -i -i . i T i testing thermal death-point, mes could be enumerated. In order to discover whether all the organisms have been killed the con¬ tents of the bulb should be emptied, preferably into a fluid medium composed of equal parts of litmus milk and broth (Harris). Methods for Testing and Standardizing Disinfectants.—The earlier attempts to determine the efficiency of disinfectants were carried out in a very simple fashion. Koch tested the action of disinfectants on anthrax spores by placing in the disinfectant solu¬ tion silk threads which had been dipped in an emulsion of the spores and dried. The threads were then washed and laid upon the sur¬ face of agar. Hill2 devised a simpler and more exact method of preparing test objects. Sterilized glass rods are dipped to a depth of 1 inch into forty-eight-hour-old broth cultures of the organism to be used in the test. The rods are then placed in test-tubes fitted with cotton plugs, carefully dried in the thermostat, and immersed in the disinfectant solution for accurately timed periods, varied as desired. Each rod, on removal, is gently but thoroughly washed 1 Eijkman: Centralbl. f. Bakt., II, 1909, 22, p. 508. 2 Hill: Rep. and Papers, Amer. Pub. Health Assoc., 1898, 24, p. 264.
    digitised image 1
    digitised image 2
    digitised image 3