CHAPTER V. 



FERMENTATIONS AND THE ACTION OF 

 ENZYMES. 



I. WHEN barley grains are supplied with an adequate 

 amount of water and kept warm they begin to germinate. 

 The embryo plant within develops and its root and 

 stem break their way out of the grain. At the same 

 time the starch of the floury part or endosperm is 

 changed into sugar, the sweet taste of which can be 

 recognized in the sprouted grain. The change of the 

 starch into sugar is brought about by the action of a 

 peculiar nitrogenous compound secreted by the cells of 

 the embryo plant. This substance, known as diastase 

 is an example of an extensive class of bodies termed 

 ferments or enzymes, which are produced in various organs 

 of living plants and animals. It is found in all germinat- 

 ing seeds, tubers, and other parts of plants which contain 

 starch, and serves the purpose of changing this solid 

 reserve-product into soluble sugar and a gum-like sub- 

 stance, dextrin, which are able to diffuse through the 

 body of the plant to wherever nutrition and growth are 

 going on. 



2. A great many kinds of enzymes are known : some 

 of them have a specific action on certain kinds of sugars, 

 others are concerned with chemical changes in proteins, 

 urea, cellulose, and many other organic compounds. 



While some of them, such as pepsin and trypsin men- 



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