. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . tion at 100° C. or at 60°to 80° C, and sterilization by steam underpressure. Filtration. — This method is resorted towhere the application of heat will inj ure thesolution, as in the case of some sugars, orwhere the necessary amount of heat wouldcause coagulation, as in the case of tissueextracts or serum. Various types of filtersmade of unglazed porcelain or compresseddiatomaceous earth are used. Types of thesefilters are the Berkefeld, Pasteur, Chamberland,and Doulton filters. The bacteria are he
. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . tion at 100° C. or at 60°to 80° C, and sterilization by steam underpressure. Filtration. — This method is resorted towhere the application of heat will inj ure thesolution, as in the case of some sugars, orwhere the necessary amount of heat wouldcause coagulation, as in the case of tissueextracts or serum. Various types of filtersmade of unglazed porcelain or compresseddiatomaceous earth are used. Types of thesefilters are the Berkefeld, Pasteur, Chamberland,and Doulton filters. The bacteria are heldback because of the fineness of the grades of fineness are procurable insome brands, and on this depends the rapidityof filtration. In any case the permeabilityof the filter should be tested before use byfiltering a broth culture of some small micro-organism, such as Bacillus prodigiosm. Before filtration the fluid to befiltered should be rendered as clear as possible by filtration through paperor if necessary through paper pulp. The latter is prepared by soaking torn-up. Fig. 31.—Filter pump for attach-ment to water faucet. 94 THE CULTIVATION OF MICROORGANISMS filter paper in water and then placing a layer in a porcelain filter, over a per-forated porcelain plate, draining off the water and packing the layer depth of the layer will depend on the fluid to be filtered, its density, andthe finexiess of the particles to be removed. This should be fastened in theneck of a filtering flask and suction applied to hasten the filtration. Similarresults may be obtained by filtration through sand. The filtration through, a filter candle (the size selected will depend on theamount to be filtered) is accelerated by the use of suction or may be secured by the use of a filter pump attached to the hydrantor other types of suction apparatus. Pressure may be obtained by air underpressure from an installed system or by a hand pump and cylinder to
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