PRODUCED BY ALCOHOLIC FERMENTS. 199 



in the first of these the fermentation was carried out with 

 Carlsberg bottom yeast No. I ; in the second, with a mixture 

 of this with Sacch. Pastorianus III. ; in the third, with Carls- 

 berg bottom yeast No. 2 ; and in the fourth, with a mixture 

 of the latter species with Sacch. Pastorianus III. The main 

 result obtained was that the beer produced with the help of 

 Carlsberg bottom yeast No. 2, was only faintly opalescent, 

 whilst the beer from the No. I yeast showed a marked 

 opalescence. The beer which had been fermented with the 

 mixture of Carlsberg bottom yeast No. 2 and Sacch, Pas- 

 torianus III. was bright at racking, whilst that fermented 

 with the mixture of Carlsberg bottom yeast No I and Sacch. 

 Pastorianus III. was rather strongly opalescent, though in a 

 much less degree than the beer from the first vessel. Sacch. 

 Pastorianus III. had thus produced the effect on the opal- 

 escent beer which was previously mentioned. 



The most probable explanation of these varying results 

 is, that the worts with which I experimented at different 

 times varied in their composition. The experiments have, 

 at any rate, shown that Sacch. Pastorianus ///., which under 

 certain conditions can play the part of a dangerous disease 

 yeast, can under others act as a curative. We have further 

 seen that wort may be so constituted that it does not require 

 the customary aeration which has hitherto been regarded as 

 perfectly necessary for the attainment of a good fermentation 

 and of a bright beer. With regard to the importance of 

 aeration, our knowledge is still very slight, and a thorough 

 investigation of this subject would, therefore, be of great 

 value. I have given the above results in this place, as I be- 

 lieve that there will not be another opportunity of returning 

 to the subject. 



Whilst speaking of variations in the activity of yeasts, 

 I may here also mention that the addition of the same amount 

 of a disease yeast produced very marked ill effects in some of 

 my experiments, and only very feeble effects in others ; and yet 



