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.

    29/830 page 27
    media; media in bulk should be heated for fifteen to twenty minutes. Care is necessary in the manipulation of the autoclave. (1) Baskets of tubes or flasks should not be piled on top of one another so that the stoppers become wet from the dripping. (2) All air should be allowed to escape before screwing down the stop-cock, as a mixture of steam and air does not reach the temperature indicated by the gage. (3) The pressure should be allowed to drop to zero before the stop-cock is opened, as a sudden removal of pressure may cause an explosive evolution of steam which will blow the stoppers and media out of the flasks and tubes. (4) In using an autoclave connected directly with a steam pipe care should be taken to see that the pressure is increased very gradually from zero to 15 pounds, other¬ wise the media in tubes and particularly that in flasks will not be maintained long enough at the temperature necessary to insure bacterial destruction. Gas-heated autoclaves work so slowly that there is no difficulty of this nature. The autoclave is much used for sugar-free broth, agar, milk and gelatin, and for sterilizing test-tubes, apparatus, and discarded cultures. In many laboratories it is used for broths containing the simpler carbohydrates. A difference of opinion exists as to the desirability of such a procedure. The more complicated carbohy¬ drates and most body fluids are best sterilized by the discontinuous method. In the preparation of Loffier’s blood-serum it was the practice for many years to sterilize in an inspissator at 53 to 70 C., but this may be done in the autoclave with good results and in a shorter time, provided sufficient care is taken to raise the medium slowly to the temperature of boiling water. In this way the air is driven from the medium before coagulation. Immersion of the tubes of blood-serum in warm water for half an hour before steriliz¬ ing, is advised. Discontinuous Sterilization.—As just stated, certain kinds of media become to some degree unfit for bacteriologic work if sub¬ jected to the high temperature reached in the autoclave. The use of a lower temperature is hence desirable. Most bacteria are quickly killed by boiling. A serious drawback, however, to the use of simple boiling is the fact that very resistant bacterial spores are sometimes not killed even when boiled for several hours. The method of discontinuous sterilization is consequently adopted in some cases. Any simple apparatus may be used for this purpose,
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