STUDIES ON FERMENTATION. 349 



less effective, according as the liquid is more or less shallow. 

 Worts and yeasts being impure, that is containing the germs 

 of foreign ferments, those germs Avould have time to germinate 

 in the fermenting vessels during the delay that the want of 

 aeration in the wort would cause in the development of the 

 yeast. We are aware that several inventions have been pro- 

 posed to do away with the coolers, and we feel convinced 

 that the object has been to remedy irregularities in fermenta- 

 tion. Considei'ing the facts which we have published * on the 

 development of yeast in the presence of air, and its inactivity 

 in non-aerated media, such inventions ought to be supplemented 

 by some means of further aeration for the prevention of the 

 mischief that they must otherwise cause. In the existing 

 process of brewing, the employment of coolers is a necessity. 



The influence of the air on the vital action of the yeast may 

 be proved in ways innumerable. The following is an experi- 

 ment which we have often carried out with surprising results. 

 A fermentation is going on ; we draw off the liquid as rapidl}'' 

 as we please, and pour it back again into the vessel immediately. 

 Within an hour we find a marked increase in the fermentation, 

 evidenced by the liberation of a greater quantity of carbonic 

 acid gas. This experiment may be performed with especial 

 ease if we use the fermenting apparatus that we have described, 

 for, by fitting a gas measurer to the escape tube a b c d e f g, the 

 number of litres produced before the drawing ofi" of the liquid 

 may be compared with those obtained after. The least physical 

 change in the running of the fermenting liquid whilst it is being 

 drawn oft', modifies the efiect in question ; such as change in 

 the diameter of the stream, the height from which it falls, its 

 greater or less scattering in falling, all influence it. Again, 

 as might be expected from such results, corresponding modifi- 

 cations take place in the cells of yeast which come under the 

 influence of the air. They become firmer in aspect and outline, 

 their plasma becomes fuller, assumes a younger and more 



* Pasteur, Comx^tes rendun de VAcademie des Scieiices, vol. Hi. p. 1260, 

 and Etudes sur le Yin, 2nd Edition, p. 277. 



