A textbook of bacteriology : including the etiology and prevention of infective diseases and a short account of yeasts and moulds, haematozoa, and psorosperms / Edgar M. Crookshank.

  • Crookshank, Edgar M. (Edgar March), 1858-1928.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: A textbook of bacteriology : including the etiology and prevention of infective diseases and a short account of yeasts and moulds, haematozoa, and psorosperms / Edgar M. Crookshank. Source: Wellcome Collection.

    190/845 (page 141)
    The simplest method for examining the organisms in air consists in exposing plates of glass or microscopic slides coated with glycerine, or with a mixture of glycerine and grape sugar, which is stable, colourless, and transparent. Nutrient gelatine spread out on glass plates may be exposed to the air for a certain time, and then put aside in damp chambers for the colonies to develop. Sterilised potatoes, prepared in the usual way, may be similarly exposed. In both the last-mentioned methods separate colonies develop, which may be isolated, and pure cultivations carried on in various other nutrient media. Nutrient gelatine has also been employed in the special methods of Koch and Hesse. Koch's Apparatus.—This consists of a glass jar, about six inches high, the neck of which is plugged with cotton-wool. In the interior is a shallow glass capsule, which can be removed by means of a brass lifter. The whole is sterilised by exposure to 150° C. for an hour in the hot-air steriliser. The nutrient gelatine in a stock-tube is liquefied, and the contents emptied into the glass capsule. The jar is exposed to the air to be examined for a definite time, the cotton-wool plug replaced, and the apparatus set aside for the colonies to develop. Hesse's. Apparatus.—The advantage of this apparatus is that it enables the experimenter to examine a known volume of air. A glass cylinder, 70 cm. long and 3*5 cm. in diameter, is closed at one end by an india-rubber cap, perforated in the centre. Over this fits another cap, which is not perforated. The opposite end of the cylinder is closed with a caoutchouc stopper, perforated to admit a glass tube plugged with cotton-wool. The tube can be connected by means of india-rubber tubing with an aspirating apparatus, which consists of a couple of litre-flasks, suspended by hooks from the tripod-stand which supports the whole apparatus. The cylinder, caps, and plug are washed with solution of carbolic acid,, and then with alcohol. After being thus cleansed, 50 cc. of nutrient gelatine are introduced, and the whole sterilised by steaming for half an hour for three successive days. After the final sterilisation, the cylinder is rotated on its long axis, so that the nutrient medium solidifies in the form of a coating over the whole of the interior. When required for use, the cotton-wool plug is removed from the small glass tube, and the latter connected with the upper flask by means of the india-rubber tubing. The apparatus is placed in the air which is to be examined, the outer india-rubber cap removed from the glass cylinder, and the upper flask tilted until the water begins to flow into the lower one.