WHAT IS THE PURE YEAST OF PASTEUR? 143 



In C, Carlsberg bottom yeast No. I, Carlsberg bottom yeast No. 2, 

 Sacch. Pastorianus /., Sacch. Pastorianus III., Sacch. ellipsoideus II. 



In D, Sacch. cerevisia /., Sacch. Pastorianus /., Sacch. Pastorianus 

 III., Sacch. ellipsoideus II. 



After the flasks had received the above mixtures of yeasts, they were 

 set aside at the ordinary room-temperature and after two days they 

 were well shaken and average samples from each were introduced into 

 fresh flasks containing some of the same sugar solution. Five cultures 

 were prepared in the manner described in the first experiment, and 

 these were left undisturbed for two days. The cultures contained in the 

 fourth and fifth flasks were tested, the fourth after eight, and the fifth 

 after ten days, calculated from the commencement of the experiment. 

 This was done in both cases by well shaking the flasks so as to mix the 

 yeast with the sugar solution, and then introducing average samples into 

 a series of flasks containing beer wort. The flasks from which the 

 samples had been withdrawn were then left at rest for a short time until 

 the remainder of the yeast had settled to the bottom ; the liquid was 

 then poured off as completely as possible, and in its place a suitable 

 quantity of wort was introduced. In this way it was not only possible to 

 work with average samples, but all the yeast present in the sugar solu- 

 tion of the corresponding culture was, so to speak, collected in the two 

 series of flasks, and the last series containing the wort received scarcely 

 any of the strong acid liquid. The importance of this may here be 

 emphasised, where it is a question of bringing about the multiplication 

 of yeast cells which have become enfeebled. In all cases sterilised 

 liquids were employed and the introduction of foreign organisms from 

 without was carefully guarded against. 



If the described treatment with the solution of cane sugar and 

 tartaric acid had really effected a purification, these flasks with the 

 cultures in wort must have contained the purified brewery yeast freed 

 from the disease germs originally present. Accordingly, we must, there- 

 fore, expect to find in the cultures from A a pure growth of the brewery 

 yeast Sacch. cerevisice /., in the cultures from B a pure growth of the 

 Carlsberg bottom yeast No. I and No. 2, in the cultures from C, also 

 the Carlsberg bottom yeast No. I and No. 2, and in the cultures from 

 D a pure growth of Sacch. cerevisice I. The result, however, was a very 

 different one. 



The cultures were placed in an incubator at a temperature of 26 C., 

 but only those flasks which contained the yeasts from A and B, and 

 which had been submitted " to the described treatment in the sugar 

 solution during eight days, showed signs of development ; all the other 

 cultures must be regarded as having perished ; even after they had 

 stood for several weeks there was no sign of life. The flasks in which 

 growth had occurred showed distinct low-fermentation phenomena, and 



