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LOUIS PASTEUR 



air at the moment when the yeast is added. Manufac- 

 tories have been erected in which the manufacture of 

 yeast is almost exclusively carried on. The saccharine 

 worts, after the addition of yeast, are left to themselves, 

 in contact with air, in shallow vats of large superficial 

 area, realizing thus on an immense scale the conditions of 

 the experiments which we undertook in 1861, and which 

 we have already described in determining the rapid and 

 easy multiplication of yeast in contact with air. 



The next experiment was to determine the volume of 

 oxygen absorbed by a known quantity of yeast, the yeast 

 living in contact with air, and under such conditions that 

 the absorption of air was comparatively easy and abundant. 



With this object we repeated the experiment that we 

 performed with the large-bottomed flask (Fie. 4), employ- 

 in a vessel shaped like Fig. B (Fie. 7), which is, in point 

 of fact, the flask A with its neck drawn out and closed 



FIG. 7 



in a flame, after the introduction of a thin layer of some 

 saccharine juice impregnated with a trace of pure yeast. 

 The following are the data and results of an experiment 

 of this kind. 



We employed 60 cc. (about 2 fluid ounces) of yeast- 

 water, sweetened with two percent, of sugar and im- 

 pregnated with a trace of yeast. After having subjected 

 our vessel to a temperature of 25 C. (77 F.) in an 

 oven for fifteen hours, the drawn-out point was brought 

 under an inverted jar filled with mercury and the point 

 broken ofif. A portion of the gas escaped and was collected 

 in the jar. For 25 cc. of this gas we found, after absorp- 

 tion by potash 20.6, and after absorption by pyrogallic acid, 

 17.3. Taking into account the volume which remained free 

 in the flask, which held 315 cc., there was a total absorption 



