250 HISTORY OF SACCHAROMYCETES IN NATURE. 



ported from the soil to the fruit, Hansen ascribes the principal 

 rdle to the wind ; though, both in his first and subsequent 

 treatises he remarks on the great importance of rain, insects and 

 other animals in this connection, the transference of cells from one 

 fruit to another being attributed to insect agency. A powerful 

 storm of rain may splash up the wet soil, accompanied by the 

 yeast cells, on to the fruit of low- lying plants, such as strawberries. 



1 Whilst the action of insects as conveyers of infection is restricted 

 to a short period in the year not only in the vicinity of Copen- 

 hagen, where Hansen's researches were carried on, but also 

 throughout the greater part of Europe the wind continues to act 

 all the year round, enormous numbers of the cells being carried up 

 in clouds of dust and deposited on the fruit. The researches also 

 show that this life history is the normal one for the yeast in 

 question, and that the cells soon die when deposited on unripe 

 fruit, owing as was ascertained by HANSEN (X.) to the fact that 

 the fungus has a very low power of resisting drought and the 

 action of the sun's rays. 



We will now turn to the question of the life history of the true 

 Saccharomycetes. When Hansen commenced his investigations 

 in this direction there had already been published a series of 

 researches by Brefeld and Pasteur running contrary to the ideas 

 which formed his starting-point. 



BREFELD (XVII.) formed the opinion that yeast cells not only 

 reproduced in the alimentary canal of the animal organism, but 

 that their chief breeding-place and habitat was the excrement of 

 herbivorous animals. Hansen showed that this is incorrect. 



From the time of the first researches on the fermentation of 

 wine, it was a recognised fact that ripe and especially damaged 

 grapes are rich in yeast cells at gathering time, and it naturally 

 followed that the yeast cells would find their way into the soil 

 with the fallen grapes or when swilled off by rain. PASTEUR 

 (XXX. and XVIII.), however, concluded from his experiments 

 that the cells could not live long in the soil, and that the latter 

 therefore could not form their winter habitat, though he gave no 

 hint as to what actually constitutes the latter. 



HANSEN (LVII.) adopted two methods in his researches : partly 

 the analysis of samples of soil and other natural substrata, 

 including the dust in the air, and partly the sowing of certain 

 species in the soil under natural conditions. The results showed 

 that true Saccharomycetes are to be found in the soil and the air 

 at all periods of the year, but most abundantly when the sweet, 

 juicy fruits are ripe. The inoculation experiments were performed 

 with Sacch. cerevisice, Sacch. ellipsoideus and Sacch. Pastor ianus, 

 the yeasts being sown in sterilised soil, placed in flower-pots 

 embedded in the ground out of doors. Here it was proved beyond 

 dispute that the cells live from one fruit harvest to another ; and 

 at the same time the observation was made (LVIII.) that the cells 



