AIR-GERMS AND SPONTANEOUS GENERATION.
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could be kept for an indefinite time in the stove, without giving rise to the smallest production of mould or infusoria. The milk preserves its taste, its smell, and all its properties; and the atmosphere of the flask is only slightly modified in its composition. This difference between
Fig. 4.—M. Pasteur's Apparatus for Studying the Resistance of Germs and Spores to the Temperatures more or less Elevated.
milk and urine, or sweetened yeast-water, must be attributed to the alkaline condition of the former medium, whereas the two others are acid. In fact, if we previously neutralize the acid of the sweetened yeast-water, by means of calcium carbonate, we obtain organisms under the same conditions of the experiment as those under which they were not before developed.