. Manual of bacteriology. Bacteriology. 30 METHODS OF CULTIVATION OF Fig. 3, — Koch's steam steriliser. narily used is "Koch's steam steriliser" (Fig. 3). This consists of a tall metal cylinder on legs, provided with a lid, and covered externally by some bad conductor of heat, such as felt or asbestos. A perforated tin diaphragm is fitted in the interior at a little distance above the bottom, and there is a tap at the bottom by which water may be sup- plied or withdrawn. If water to the depth of 3 inches be placed in the interior and heat applied, it will quickly boil, and
. Manual of bacteriology. Bacteriology. 30 METHODS OF CULTIVATION OF Fig. 3, — Koch's steam steriliser. narily used is "Koch's steam steriliser" (Fig. 3). This consists of a tall metal cylinder on legs, provided with a lid, and covered externally by some bad conductor of heat, such as felt or asbestos. A perforated tin diaphragm is fitted in the interior at a little distance above the bottom, and there is a tap at the bottom by which water may be sup- plied or withdrawn. If water to the depth of 3 inches be placed in the interior and heat applied, it will quickly boil, and the steam streaming up will surround any flask or other object standing on the diaphragm. Here no evaporation takes place from any medium as it is surrounded during sterilisation by an atmosphere saturated with water vapour. It is convenient to have the cylinder tall enough to hold a litre flask with a funnel 7 inches in diameter standing in its neck. The funnel may be supported by passing its tube through a second per- forated diaphragm placed in the upper part of the steam chamber. With such a " Koch " in the laboratory a hot-water filter is not needed. An even more serviceable steriliser is that known as the Arnold steam steri- liser, which, by its peculiar con- struction, effects a greater saving in the time necessary to develop steam than does a similar sized Koch apparatus. As has been said, one and a half hours' steam- ing will sterilise any medium, but in the case of media containing gelatin such an exposure is not practicable, as, with long boiling, gelatin tends to lose its physical property of solidification. The method adopted in this case is to steam for a quarter of an Jioiir on each of three succeeding days. This is a modification of what is known as " Tyndall's intermit- tent ; The fundamental principle of this method is. Please note that these images are extracted from scanned page images that may have been digitally enhance
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