276 MICRO-ORGANISMS AND FERMENTATION. 



small lemon-shaped wine yeasts. S. anomalus and 8, mem~ 

 brancefaciens are especially resistant to the effect of drying. 

 They are, therefore, found at great distances from the primary 

 habitats. In this way the fact may also be explained that 

 fewer yeast species are sometimes found in the soil of vine- 

 yards than in the neighbouring meadows. The cells in the 

 vineyards are dried up and killed, whereas in the meadows 

 where the cells are protected from drying, life is maintained, 

 and the cells multiply. In such places cells also occur during 

 the hot season of the year, and here their propagation goes- 

 on most vigorously. Where the ground is subject to drought 

 the variation brought about in the course of years may be 

 altogether extraordinary. 



The soil must, therefore, be considered the chief habitat of 

 yeast at every time of the year. They are carried from the 

 earth by means of wind and rain, as well as by the action of 

 insects and other creatures, to the sweet juicy fruits, where 

 they multiply vigorously ; a few fall to the earth again, whilst 

 others are carried to secondary places of incubation. When 

 the fruit is ripe the wild yeasts thus strongly developed find 

 their way into the fermentation industry. It is only if they are 

 allowed to remain, to multiply, and to obtain a secure footing, 

 that they are capable of bringing about any disturbance in the 

 industry. Otherwise they are immediately suppressed by the 

 large quantity of the culture yeast added to the nutritive liquid. 



During their development on grapes and other juicy fruit 

 the yeast cells compete for nutrition with many other organ- 

 isms, including bacteria and moulds. These observations led 

 Wortmann to adopt the view that the true importance of 

 alcoholic fermentation is biological. Most of the competitors 

 of yeast can multiply much more rapidly, and would soon 

 suppress it if no means existed for restricting their growth. 

 This means is supplied by the alcohol produced by the yeast 

 cells, whereby they are able to poison their enemies. Wort- 

 mann showed how the poisonous action of alcohol is apt to- 

 support yeast in competition with other organisms. During 

 the early stages of the development of yeast in must a surface 

 growth of various organisms can be observed. Amongst these 

 the small apiculate yeast is especially prominent, and this soon 



