. Manual of bacteriology. Bacteriology. STERILISATION BY MOIST HEAT. 29. Fig. 2.—Hot-air steriKseir. A. (2) Sterilisation by Dry Heat in a Hot-air Chamber. — The chamber (Fig. 2) consists of an outer and inner case of sheet iron. In the bottom of the outer there is a large hole. A Bunsen is lit beneath this, and thus plays on the bottom of the inner case, round all of the sides of which the hot air rises and escapes through holes in the top of the outer case. A thermometer passes down into the interior of the cham- ber, halfway up which its bulb should be situated. It is found, as a matter of
. Manual of bacteriology. Bacteriology. STERILISATION BY MOIST HEAT. 29. Fig. 2.—Hot-air steriKseir. A. (2) Sterilisation by Dry Heat in a Hot-air Chamber. — The chamber (Fig. 2) consists of an outer and inner case of sheet iron. In the bottom of the outer there is a large hole. A Bunsen is lit beneath this, and thus plays on the bottom of the inner case, round all of the sides of which the hot air rises and escapes through holes in the top of the outer case. A thermometer passes down into the interior of the cham- ber, halfway up which its bulb should be situated. It is found, as a matter of experience, that an ex- posure in such a chamber for one hour to a temperature of 170° C, is sufficient to kill all the organisms which usually pollute articles in a bacteriological laboratory, though circumstances might arise where this would be insufficient. This means of sterilisation is used for the glass flasks, test-tubes, plates, Petri's dishes, the use of which will be described. Such pieces of apparatus are thus obtained sterile and dry. It is advisable to put glass vessels into the chamber before heating it, and to allow them to stand in it after sterilisation till the tem- perature falls. Sudden heating or cooling is apt to cause glass to crack. The method is manifestly unsuitable for food media. B. Sterilisation by Moist Heat. B. (i) By Boiling. —The boiling of a liquid for five minutes is sufficient to kill ordinary germs if no spores be present, and this method is useful for sterilising distilled or tap water which may be required in various manipulations. It is best to sterilise knives and instruments used in autopsies by boiling in water to which a little sodium carbonate has been added to prevent rust- ing. Twenty minutes' boiling will here be sufficient. The boil- ing of any fluid at 100° C. for one and a half hours will ensure sterilisation under almost any circumstances. B. (2) By Steam at 100° C.— This is by far the most useful means of sterilisa
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