144 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



possible to acclimatise certain yeasts by growing them in a 

 mixture of this sugar and dextrose, after which they will attack 

 galactose readily. 



The results of the experiments on the fermentation of 

 different sugars by yeasts lead to the conclusion that the 

 enzyme of the yeast combines with the sugar, and that the 

 velocity of formation of carbon dioxide is determined by 

 the rate of decomposition of the compound formed. 



It is still somewhat an open question whether there are 

 present in yeast cells a large number of enzymes, each capable 

 of exerting its own specific action, or whether only a few 

 enzymes are present, and that the same enzyme can promote 

 different chemical actions. 



From the foregoing pages it is evident that the chemistry 

 of the yeast cell has been a fruitful subject of inquiry. The 

 researches that have been considered are of great scientific 

 interest in showing the complexity of the reactions which take 

 place even under the comparatively simple conditions afforded 

 by a single cell of yeast. 



They have also a very important bearing on the fermenta- 

 tion industries, which have for their object the preparation of 

 various forms of alcoholic beverages. 



While it is impossible usefully to consider these in this 

 book, owing to the complexity of their purely technical detail, 

 mention should be made of the great advance made in the 

 brewing industry by the use of pure cultures of yeasts intro- 

 duced by Hansen. 



His method of obtaining these on a small scale has been 

 described in Chapter II. By successive inoculation into 

 larger and larger volumes of sterile wort it has been possible 

 to brew beer by means of one culture only. The brewer is 

 enabled thus to conduct the process of fermentation under 

 rigidly controlled conditions. 



