Page:Popular Science Monthly Volume 9.djvu/114

96 Fig. 1 applies to dust collected from the 25th to the 26th of June, 1860; Fig. 2 to dust from the very intense fog of January, 1861.

It was not enough to discover with the microscope organic particles mixed with amorphous substances, but it was necessary to prove that these particles really consisted of fertile germs, capable of producing the infusoria which are developed in such abundance in organic liquids exposed to the air. For this purpose, M. Pasteur arranged the experiment in the following manner:

Into a flask capable of containing from 15 to 18 cubic inches, he introduced 6 to 9 cubic inches of albuminous saccharine water, prepared in the following proportions:

Water, 100;

Sugar, 10;

Albuminoid and mineral matter from beer-yeast, .2 to .7.

The neck of the drawn-out neck-flask communicated with a platinum tube, as shown in Fig. 3. In this first stage of the experiment the T-shaped tube with three stopcocks is removed, and its place supplied by a simple India-rubber connecting-piece. The platinum tube is raised to a red heat by means of a small gas-furnace. The liquid is boiled for two or three minutes, and is then allowed to grow completely cold. It is filled with common air, at the ordinary pressure of the atmosphere, but which has been wholly exposed to a red heat; then the neck of the flask is hermetically sealed.

This, being thus prepared and detached, is placed in a stove at a constant temperature of about 86° Fahr.; it may be kept there for any length of time without the least change in the liquid which it contains. It preserves its limpidity, its smell, and its weak acid reaction; even a very slight absorption of oxygen is mainly to be observed. M. Pasteur affirms that he never had a single experiment, which was arranged as described above, which yielded a doubtful result; while water of yeast mixed with sugar, and boiled for two or three minutes, and then exposed to the air, was already in evident process of decomposition in a day or two, and was found to be filled with bacteria and vibrios, or covered with mucors. These experiments are directly opposed to those of Messrs. Pousset, Mantegazzo, Joly, and Musset.

It is therefore clearly proved that sweetened yeast-water, a liquid very liable to be decomposed by the contact of common air, may be preserved for years unaltered when it has been exposed to the action of calcined air, after having been allowed to boil for a few minutes (two or three).

This being determined, M. Pasteur adapted, by means of an India-rubber tube, the closed point of his flask filled with sweetened