ALCOHOLIC FERMENTS. 247 



Finally, it remained to be proved that the soil is its true 

 habitat during the winter ; in order to prove this, HANSEN 

 examined dust from the most diverse places from January to 

 June, also the dried fallen fruits of many plants, and finally 

 various excrements. His seventy-one analyses gave a negative 

 result, and thus furnished the proof that the true winter habitat 

 of the ferment is the soil under the fruit trees. It retains its 

 ordinary appearance during the long winter-time, and in the 

 summer it is again carried into the air by the united action of 

 insects and wind, and, through these two means of transport, it 

 is further distributed from fruit to fruit. 



It is evident that at the time when the ferment appears in 

 abundance on the ripe fruits mentioned, it may also be carried 

 by the wind to surrounding objects and so on to unripe fruits. 

 Even in his first memoir, HANSEN stated that the rare occurrence 

 on unripe fruits might be due to the ferment quickly perishing, 

 partly from want of nourishment and partly from the drying up 

 of its cells. He subsequently proved by experiment the correct- 

 ness of this view. He stirred up with water old and young 

 cells, and placed them in thin layers, either on object-glasses 

 or on tufts of cotton-wool well teased out, which were then 

 allowed to dry under protection from the sun. In less than 

 twenty-four hours all the cells had perished. It is self-evident 

 that isolated cells lying on unripe fruit are still more unfavour- 

 ably placed than in the experiment. If, however, thick layers 

 of the cells are wrapped in cotton-wool or filter-paper, they 

 will continue to live for a long time, as they do in the earth 

 in filter-paper, for instance, for more than eight months. 



No complete investigations have been published on the life- 

 history of other alcoholic ferments. Saccharomycetes occur very 

 generally on fruits containing a sweet juice. For several years 

 HANSEN has carried on experiments similar to those described, 

 with species of Saccharomycetes which often occur in fruit 

 gardens, such as Sacch. Pastorianus 1., Sacch. ellipsoideus /., 

 also with Carlsberg bottom-yeast No. 1, and with some 

 top-fermentation beer-yeasts. He always found that yeasts 

 sown in the soil in September were alive a year later. Some 

 species had formed spores at the surface of the soil. 



The wine-yeasts belonging to the group Saccharomyces 



