ENZYMES AND OTHER FERMENTS DIGESTION. 123 



5. In the so-called fermentation of urea. 



Some of these reactions may be represented by definite equa- 

 tions. In general they correspond to the changes produced 

 in the same substances by weak acids with some variations in 

 the details. The salient points will be indicated here, leaving 

 in most cases the fuller discussion for following chapters which 

 deal with the details of digestion phenomena. 



CHANGES IN CARBOHYDRATES. 



Amylase or Diastase. Certain enzymes convert starch 

 paste into malt sugar by a reaction which is indicated by the 

 equation : 



(C 12 H 20 10 )u + (H 2 0)n =(C u HOn) 



The enzymes here active are usually described as diastases or 

 amylaseSj the terms being employed in the plural, since the 

 action is not confined to a single substance. Of these two 

 terms the word diastase is frequently employed in the broad 

 sense to include all the enzymes which act on the starches and 

 sugars formed from them, while the term amylase is employed 

 to describe the enzyme which changes starch into malt sugar. 

 In this sense it will be used here. In nature ferments of this 

 character are very widely distributed and serve very important 

 functions. They are active in the changes going on in the 

 vegetable kingdom during the growth of plants and the ripen- 

 ing of fruits, as well as in the germination of seeds. On the 

 commercial scale malt represents the best known diastase- 

 containing substance. In the animal body similar substances 

 are found in the saliva and in the pancreatic secretion. The 

 first of these is called salivary diastase or ptyalin and the sec- 

 ond pancreatic diastase or amylopsin. 



These diastases have never been secured in anything like 

 pure condition. Very active solutions which digest starch 

 quickly may be obtained by extracting ground malt with water, 

 which will be illustrated later. These solutions may be con- 

 centrated at a moderate temperature, but the activity of the 

 enzyme is destroyed by heat. A stronger product may be 



