82 STUDIES ON FEUMENTATION. 



containing some pure wort. We then placed the flask in an 

 oven, at 20° C. 



On December 21st, three days after we had sown the powder, 

 fermentation began to manifest itself by the appearance of 

 patches of froth on the surface of the wort. On December 10th 

 and 20th the yeaat was sensibly developing, although there was 

 no liberation of gas to denote the presence of actual fermentation. 

 The yeast, examined under the microscope, appeared very pure. 



On March 5th, 1873, we took another pinch of the yeast- 

 and-plaster powder from the twist of paper, and placed it in 

 a flask of pure wort, as in the foregoing experiment. 



On March 9th, that is, after having been subjected to a heat 

 of 20° C. (68° F.) in the oven for four days, fermentation began 

 to manifest itself by the appearance of patches of froth on the 

 surface of the wort. From this it was evident that the yeast 

 had not been destroyed, but only retarded in its revival. 



On July 25th, 1873 — that is, after a lapse of seven months 

 and a half — we resumed our experiments, and sowed some 

 more of the yeast-and-plaster powder in another flask of wort. 

 On August 2nd, eight days from the time of our sowing, the 

 little islets of froth appeared on the surface of the liquid. 

 Observed under the microscope, the yeast still seemed pure, 

 and resembled the original yeast ; we append a sketch, which 

 will give an idea of its shape (Fig. 15). 



:? k 



Fig. 15. 



On November 7th, 1873, we once more sowed some of the 

 powder. This time the yeast was dead ; we observed the 

 flask whicli contained it, day by day, until February 1st, 1874, 

 without detecting the sHglitest sign of fermentation or de- 

 velopment of the yeast that we had sown. On Februarj^ 1st, 

 we made a microscopical examination of the yeast, and found 



