266 APPLIED BACTEKIOLOGY 



tion of the carbon dioxide, is left as a reduced product of 

 the reaction. In most cases a part of the hydrogen is 

 removed as water, and in some cases as free hydrogen. 



Mixed Fermentations. — To this class belong a large number 

 of fermentations which form the foundations of such im- 

 portant industries as butter, cheese, and wine making, the 

 curing of tobacco, the fermentation of bread, the tanning 

 of leather, the manufacture of koumiss (fermented milk), 

 ginger - beer, indigo, etc. All these and many other im- 

 portant processes in which fermentation plays an important 

 part have yet to be thoroughly investigated. 



It is of interest in this connection to mention that much 

 work is now being done on the Continent in the way of 

 improving low-grade wines by the employment of pure 

 cultures of micro-organisms obtained from high -class 

 vintages, whereby much of the characteristic aroma and 

 bouquet of the best vintages are communicated to a con- 

 siderable extent to the poorer qualities of wine. In the 

 same way butter, cream, and cheese are being improved 

 and kept of standard quality by the same means. The 

 extension of these scientific processes will no doubt do 

 away to a large extent with the somewhat empirical and 

 uncertain methods of dairying now in vogue. 



(6) The Unorganised Ferments, or Enzymes. — These have 

 no organised structure or power of multiplication, but are 

 highly complex bodies of an albuminoid nature, which 

 possess the power of bringing about chemical changes on 

 a scale altogether out of proportion to their own mass. 

 The mode of action of these ferments is not quite under- 

 stood, but appears to be similar to the process of hydrolysis, 

 which takes place when sulphuric acid converts alcohol 

 into ether, when theoretically a given quantity of acid is 

 capable of converting an unlimited amount of alcohol. 

 These ' soluble ' ferments are divisible into a number of 



