RACES OF YEASTS 129 



The cardinal temperatures for sporulation are given and show the value 

 of such physiological data. For the differentiation of very closely related 

 races more subtle distinctions are utilized, such as the shape of the cells, 

 mode of budding, power of fermentation, and particularly the ability to 

 break up various sugars of closely allied chemical structure. 



Some of the natural species of yeasts are destitute of spores. 

 Hansen (104), guided by the attempt to cultivate a sporeless breed 

 of anthrax bacilli, endeavoured to induce the asporogenous condition 

 among spore-bearing yeasts by similar means, i. e. by cultivation at 

 high temperature. His experiments were successful ; sporulation was 

 suppressed and did not appear in subsequent generations. At the same 

 time the fermenting powers of the yeast were slightly altered. It seemed 

 at first that the attempt to obtain sporeless races had been more successful 

 among the yeasts than with the bacteria, but subsequent observations 

 showed that the phenomena were the same in both cases. When mixed 

 with earth, the sporeless varieties of yeast died out in one year, whereas 

 the unaltered spore-bearing form of the same species lived for three 

 years under the same conditions. This fact alone shows that a general 

 weakening of the organism had set in, and other signs of degeneration 

 were not wanting. But although the attempt to produce races of yeast 

 with new morphological characters has not been an unimpeachable success 

 it is undoubtedly possible to obtain races with more or less permanently 

 altered physiological functions — races that produce more (or less) alcohol 

 than the parent form, or in which the by-products of fermentation are 

 different or present in different proportions. In the brewing industries (105) 

 hundreds of such races have already arisen, and give to each particular 

 kind of beer its specific flavour, while Hansen's investigations have led 

 to the application to yeasts of the methods of pure culture, so that the 

 most desirable varieties can be artificially propagated. 



The wine yeasts also include innumerable races. Almost every kind 

 of wine has its own species of Saccharomyces. The secondary products 

 of fermentation are of great importance, particularly the aromatic sub- 

 stances (ethers) which give the 'bouquet.' But, whilst these zymogenic 

 products are undoubtedly influential in determining the flavour of the 

 wine, it must not be forgotten that the aromatic constituents of the grape 

 itself are of still more importance. The pure culture of yeasts of known 

 fermentative properties is a great step forwards, but it is not everything. 

 It will never be possible, for instance, to make a sour inferior Rhine wine 

 into an expensive Johannisberger merely by the use of the Johannisberg 

 yeast (105). 



In the old methods of wine-making the fermentation was left to 

 ' go on of itself ' ; in other words, it was left to the yeasts accidentally 

 present in the grape juice. The grapes hanging on the vines always have 



FISCHER K. 



