WHAT IS THE PURE YEAST OF PASTEUR? 149 



cultivation in the sugar solution the yeast had not yet experienced 

 so marked a change, and the brewery yeast still preponderated. 



The second series of these experiments was carried out at a tem- 

 perature of about 9 C, as stated above, When the third culture in the 

 sugar solution had stood two days, an average sample was introduced 

 into a fourth flask. The yeast from the third cultivation was then intro- 

 duced >nto wort also at 9 C. In the same manner, the yeast from the 

 fourth and fifth cultivations in sugar solution, after standing the usual 

 time, was likewise cultivated in wort. In consequence of the low tem- 

 perature employed, it was only after about twelve days that a perceptible 

 development of yeast in the last-named wort culture was detected, and 

 only after fifteen days in the two others. If Pasteur's method were 

 correct, the yeast growths in these three flasks should consist, therefore, 

 of the pure brewery yeast. A contrary result was, however, also obtained 

 in this case. The brewery yeast had, namely, as in all my other experi- 

 ments , been completely suppressed by the wild y easts , and yet at the 

 beginning of the experiment these were, as stated above, only present in 

 an extremely minute proportion. The new objections brought forward 

 by Velten are, therefore, completely refuted. 



The fact that Pasteur and his collaborators recommended a method 

 which even brought about diseases in beer, clearly shows that they had 

 no knowledge of the part played by certain wild yeasts in producing 

 disease, and that the nucleus of the problem of the pure cultivation of 

 yeast had altogether escaped their notice. I have, therefore, been com- 

 pelled to conduct these researches on new lines, and my opponents have 

 not been able to pardon me for this. In the attacks, whether small or great, 

 which have been directed against me, a wrath is manifest that the new 

 reform came from Denmark and not from France. 



3. The above experiments have shown that the brewery 

 bottom yeasts which were investigated are unable to resist 

 the treatment with the tartaric acid and sugar solution ; the 

 top-fermentation yeast Sacch. cerevisice /., appears to possess 

 a somewhat higher resistive power, but this species was 

 also suppressed by the wild yeasts. The disease yeasts 

 Sacch. Pastorianus I. and Sacch. ellipsoideus //., exhibited 

 the greatest resistive power. It is possible that some- 

 what different results might be obtained under other 

 conditions. 



The objections which have been brought forward against 

 the employment of tartaric acid for the preparation of pure 

 yeast, also apply in principle to other similar substances and 



