Another method is suggested to us by the curious results of which we have already spoken, obtained by sowing yeasts in a wort rendered acid and alcoholic by the addition of bi-tartrate of potash and alcohol. Experience proves that many disease-ferments find great difficulty in withstanding a succession of growths in wort to which 1-½ per cent. of tartaric acid and from 2 to 3 per cent. of alcohol have been added. Such a mixture, however, is equally well adapted to the requirements of _saccharomyces pastorianus_, and we must always assure ourselves that this organism has not taken the place of the yeast we are endeavouring to purify. Growths at a very low temperature are of great help in enabling us to get rid of all ferments that are foreign to “low” yeast, and should be resorted to in all cases where this yeast is to be purified. Another method of purification, which is perhaps quicker, although inferior in other respects, consists in the employment of carbolic acid—that is to say, in purifying our yeast by successive growths, we may add to every 100 c.c. (3-½ fluid ounces) of wort that we employ from ten to twelve drops of phenol water, containing 10 per cent. of the acid. The action of the phenol, which at first is invariably combined with that of the oxygen of the air, tends to destroy the vitality of many of the cells sown, involving to some extent also the yeast which we are interested in preserving. But amongst the number of cells that are affected those which are less abundant, that is to say, those which are present as impurities, are paralyzed relatively in much greater proportion. If the acid does not destroy them it greatly checks their development, and the cells of yeast, which multiply continuously in vast numbers (for the fermentation goes on in spite of the phenol, if this is added in small quantity), gradually choke the foreign germs in a succession of growths.