CARBOHYDRATES 59 



concentrated sulphuric acid carefully poured down the side of 

 the test tube so that it will form a layer at the bottom of the 

 tube, a violet or reddish ring will form at the juncture of the 

 two liquids. This test will detect not only free carbohydrate, 

 but also carbohydrate in combination with other substances. 

 The reaction is so delicate, however, that it will be given by very 

 small traces of carbohydrate material, even fibers of filter paper 

 (cellulose) so that as a general test it is more valuable in a 

 negative than in a positve result. A negative Molisch reaction 

 is good evidence that carbohydrates are absent, whereas a posi- 

 tive test may be due to the presence of filter paper or other 

 casual impurities. As little as 0.2 mg. filter paper is said to 

 give a strong reaction. 



Fermentation Enzymes 



Under the influence of certain microorganisms the carbohy- 

 drates undergo a process known as fermentation, which consists 

 in the breaking up of the carbohydrate molecule to form a 

 variety of simpler compounds. The nature of the products de- 

 pends upon the character of the particular organism respon- 

 sible for the decomposition. Thus the carbohydrate may form 

 carbon dioxide and alcohol, a process known as alcoholic fer- 

 mentation. Or it may form lactic acid, butyric acid, or still 

 other substances. In alcoholic fermentation we may represent 

 the process as follows: 



C 6 H 12 6 -*2 C 2 H 5 OH+2C0 2 



but in reality there are intermediate steps the character of 

 which is but imperfectly understood. The changes brought 

 about in the sugar in these reactions are due to the fact that the 

 microorganisms involved contain or secrete compounds which 

 have the power of breaking down the sugar. We know a great 

 many of these substances, and their activities are by no means 

 limited to the breaking down of sugars. To them has been given 

 the name of enzymes and different members of this class of sub- 

 stances have the power of bringing about the most widely vary- 



