274 MICRO-ORGANISMS AND FERMENTATION. 



in the air. He further proved that the wine-yeast cells may 

 occur in soil at a depth of from 20 to 30 cm. 



In 1897, Wortmann's researches, recorded in his work on 

 the preparation of wine, were directed to determining the 

 behaviour of wine yeasts in soil at different seasons of the year. 

 The experiments were continued for two years, and consisted 

 in taking samples of soil every fourteen days from one and 

 the same part of a vineyard. By sowing the soil in sterile 

 must, he obtained an idea of the vegetation. His main 

 observation was that directly after the vintage (in November 

 and also in December) the samples of soil developed a growth 

 of yeast in must so rapidly that no other fungi were able to 

 develop. In January, February, and March also a develop- 

 ment of yeast was always obtained from the samples, but it 

 occurred more slowly. In the spring and summer the con- 

 ditions were always less favourable, and a longer period 

 elapsed before fermentation began. Some samples, indeed, 

 gave no yeast development, but only other organisms. The 

 least favourable conditions were observed in the late summer 

 (August and September), but from the time the grapes began 

 to ripen, a vigorous growth was again observed in the flask. 

 Wortmann concluded that while the wine yeast remains in 

 the soil its nutritive state is of the greatest importance. The 

 vegetation is most vigorous during the early stages, when it 

 has been enriched with cells fresh from the grapes i.e., in the 

 autumn, winter, and the beginning of spring whereas during 

 the summer, the most favourable period for vegetation gener- 

 ally, its power is constantly diminishing, the cells having drawn 

 upon their reserve material. According to this view, the yeast 

 is dependent upon its own body-material during its habitat 

 in the soil. The lower temperature ensuing after the vintage 

 allows metabolism to go on so slowly that it enables the 

 cells to maintain life throughout the winter and spring. 



At the beginning of summer, with increasing temperature, 

 the cells rapidly assimilate the remainder of the reserve 

 substance, and consequently die off slowly. The cells that are 

 still alive are weakened, and the samples of soil, therefore, 

 give a very feeble growth in the flasks. The cells are con- 

 tinuously carried by insects and other means from the soil to 



