

9 6 THE POPULAR SCIENCE MONTHLY. 



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 parti- 

 cles mixed with amorphous substances, hut it was necessary to prove 

 that these particles really consisted of fertile germs, capable of pro- 

 ducing 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, pre- 

 pared in the following proportions : 



Water, 100 ; 



Sugar, 10; 



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



The neck of the drawn-out neck-flask communicated with a plati- 

 num 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 sup- 

 plied 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 com- 

 pletely 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 con- 

 tains. 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 decom- 

 position 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). 1 



This being determined, M. Pasteur adapted, by means of an India- 

 rubber tube, the elosed point of his flask filled with sweetened yeast- 



1 M. Pasteur lias pointed out a cause of want of success, which has led many experi- 

 menters into error; by showing that the mercury of a mercurial trough is a complete 

 receptacle for living organisms, and consequently that all experiments made with such a 

 trough must necessarily induce a development of infusoria. 



