98 THE POPULAR SCIENCE MONTHLY. 



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 arrange- 

 ments 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. Pas- 

 teur : 



In all the flasks, into which dust collected from the air was intro- 

 duced 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 at- 

 mosphere. 



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 intro- 

 duced, 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 ex- 

 periment 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 dif- 

 ferent 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, 



