BIOLOGICAL RELATIONSHIPS OF YEAST. 275 



the vegetation, and those which light upon the grapes when 

 they are ripe find full nourishment, and produce a new vigorous 

 growth. Wortmann was able to confirm Miiller-Thurgau's 

 observation that no wine yeasts are to be found in a vineyard 

 which has not been worked for a long time ; they are gradually 

 killed out by exhaustion. In those wine districts where the 

 culture of grapes has been continued for centuries, the yeast 

 oells which are brought from the soil when the grapes are ripe 

 adapt themselves more and more to the excellent nutrient 

 material, and in this way specially good races of wine yeasts 

 .are developed. 



In 1903 and 1905 Hansen obtained results which differed 

 from those of Wortmann in one important point relating to 

 the condition of yeast cells during their abode in the soil which 

 the latter regarded at a state of starvation. This new and very 

 detailed research led to the result that elliptical and Pastorianus 

 forms of Saccharomyces (but not S. apiculatus) are to be found 

 throughout the year in all kinds of soil in the neighbourhood of 

 {Copenhagen. Their number diminishes, however, at a distance 

 from the orchards. A similar condition of things was found 

 by examining soil in the Harz Mountains and in the Alps. 

 The soil in vineyards is specially rich in yeast species, and the 

 greater the elevation the smaller is the number of organisms 

 found. Above a certain height no organisms are found. 



The reason for this wide distribution lies, as Hansen showed, 

 in the fact that, in addition to the normal breeding places for 

 yeast, there are others which he called secondary breeding 

 places e.g., aqueous extracts from fruit and other vegetable 

 matter and from excrement. In the former, the cells multiply 

 very rapidly, in the latter, feebly or not at all. If yeast 

 cells from sweet juicy fruit and from the upper layers of soil, 

 where they form spores, are carried by insects or by wind to 

 distant places, they may, unlike S. apiculatus, maintain life 

 even when dried, on account of their greater power of resistance. 

 In the same way they can multiply more readily in soil in the 

 aqueous extracts already referred to, and may even preserve 

 life for a longer period in presence of nothing but moisture. 

 Thus the fact is fully explained that the larger species occur 

 much more widely distributed throughout the soil than the 



