Page:Popular Science Monthly Volume 9.djvu/116

98 with the air-pump, another with the heated platinum tube, and the third with the flask, by means of the large tube which contains the smaller one with the cotton. These various parts are joined together by means of India-rubber.

The experiment is commenced by exhausting the air, after having closed the stopcock connected with the red-hot metallic tube. This being afterward opened, allows calcined air to enter the tubes slowly; this operation (exhaustion and readmission of calcined air) is repeated several times. The point of the flask is then broken off within the India-rubber, and the small tube containing the dust is allowed to slip into the flask, the neck of which is again sealed with the lamp. As an additional proof, and to obviate all objections, the same arrangements were made with similar flasks, prepared like the preceding, but with this difference that, instead of cotton charged with atmospheric dust, there was substituted a small piece of tube containing calcined asbestos (as an additional precaution, it had been ascertained that calcined asbestos, loaded with atmospheric dust, by the same means as the cotton, gave identical results).

The following are the observations obtained constantly by M. Pasteur:

In all the flasks, into which dust collected from the air was introduced—1. Organic productions began to make their appearance in the liquid after twenty-four, thirty-six, or forty-eight hours at the most. This was precisely the time necessary for the same phenomena to appear in sweetened yeast-water exposed to contact with the atmosphere.

2. The products observed are of the same kind as those which are seen to make their appearance in the liquid when left freely exposed to the air, such as mucors, common mucidines, torulacei, bacteria, and vibrios of the smallest species, the largest of which, the Monas lens, is only .000157 inch in diameter.

When the water of yeast is replaced by urine, the experiment being conducted exactly in the same manner, we always notice the absence of any change as long as atmospheric dust has not been introduced, while, with the addition of this, numerous organisms are developed, in every respect similar to those which appear and are developed in urine kept in the open air. If, on the contrary, the experiment be repeated with common milk, we may be sure that it will in every case curdle, and become putrid. We shall observe the birth of numerous vibrios of the same species, and bacteria, and the oxygen of the flask will disappear. M. Pasteur thinks that this result, so different from those observed in other liquids, arises only from the fact that milk contains germs of vibrios which resist the boiling heat of water. To prove this, he boiled milk, not at 212° Fahr., or at the usual pressure of the atmosphere, but at 230° Fahr., under a greater pressure, and he found that the flasks thus prepared, and hermetically sealed,