VOLATILE ACIDS AND ALDEHYDES. 501 



cell of the yeast is smaller in cultures that have been aerated. 

 The results of this test, however, cannot be accepted uncondition- 

 ally, the passage of air being accompanied by subsidiary effects, 

 inasmuch as it sets up vibrations in the wort liquid and thus 

 stimulates reproduction. According to RAPP (I.), the fermentative 

 activity on the other hand is diminished by powerful vibration, so 

 that the aforesaid stimulative effect is counteracted to an extent 

 that has not been precisely determined. Moreover, the air in its 

 passage carries off volatile metabolic products, including those of 

 an injurious character, thus freeing the nutrient medium from 

 poisonous constituents, to an extent varying according to circum- 

 stances. This favourable influence is absent in all the parallel 

 experiments in which a similar " rousing " with inert gas has not 

 been performed. If hydrogen (which is very difficult to obtain in 

 a perfectly pure state) be used for this purpose, it is stated by 

 KORFF (I.) that the resulting acids differ considerably from those 

 formed when in aerated cultures, a circumstance that will readily 

 be understood in view of the chemical action exerted by atmo- 

 spheric oxygen. 



The difficulty and complication of the task of investigating the 

 influence of oxygen on alcoholic fermentation by means of yeast 

 are increased by the powerful stimulus imparted by this gas to the 

 reproduction of the cells. An attempt to counteract this disturb- 

 ing factor was made by A. J. BROWN (IV.). Starting from his 

 own observation that no appreciable reproduction occurs in wort 

 pitched with a larger number of cells than can be grown therein 

 from a minimum sowing, he made large sowings in a mixture of 

 yeast water and glucose, passing either air, hydrogen, or carbon 

 dioxide through the liquid. By operating in this way it was found 

 that, whilst the number of cells remained practically unaltered 

 throughout the experiment, the amount of sugar fermented was 

 larger in the case of the aerated cultures. The conclusion 

 deduced therefrom, that a given number of cells of approximately 

 the same total weight will ferment more sugar in presence of air 

 than without, was opposed by DUCLAUX (XVIII.) on arithmetical 

 grounds, which, however, were rejected by BROWN (VII.). 



Brown's experiments need to be repeated, as was pointed out 

 by H. VAN LAER (XI.) and IWANOWSKI (I.), since the assumption on 

 which they are based conflicts with general experience. The 

 absence of any reproduction in the excessive sowing was probably 

 due to some unfavourable constitution of the nutrient medium 

 employed, a factor whose influence has been shown by the ex- 

 periments of N. VON CHUDIAKOW (I.), who supports the view that 

 oxygen has a restrictive influence on alcoholic fermentation. 

 Another circumstance left entirely out of consideration is the 

 fact that a number of cells perish during fermentation and undergo 

 dissolution, so that when the same quantity of yeast is found at the 

 beginning and end of the process, it cannot be assumed, with 



