ENZYMES AND OTHER FERMENTS - DIGESTION. 125 



we have as describing the same ferment the term glucose in 

 use, since glucose is the product formed. It is preferable to 

 employ the first designation or maltose. This enzyme belongs 

 to the class of so-called inverting ferments which convert di- 

 saccharides into monosaccharides. In this special case malt 

 sugar yields glucose: 



CuHaOii + H 2 O = 2C 6 H 12 Oe. 



This maltase is found not only in malt extract, but in vari- 

 ous yeasts and elsewhere in the vegetable kingdom. It is also 

 present in saliva, but in small amount, in the pancreas, the liver 

 and in the blood. The formation of glucose in most cases is 

 probably a secondary reaction, maltose being formed first as 

 the primary product. The general importance of this reaction 

 will be pointed out later, as it plays a very essential part in the 

 digestion of the carbohydrate foods. 



Lactase. In analog} 7 with the conversion of malt sugar 

 into glucose we have the conversion of its isomer, lactose or 

 milk sugar, into two monosaccharide groups. This is accom- 

 plished by the ferment called lactose which is found in several 

 kinds of yeast, and which appears to be distinct from the mal- 

 tase just described. The change of milk sugar is represented 

 b this reaction : 



C 12 H 22 On + H 2 = CeHxsOe + GH^Oe. 

 Glucose Galactose 



Lactose and glucose have nearly the same specific rotation, 

 [a]^^ 52. 5 for the first and 53 for the second, while for 

 the galactose it is about 83. The inversion may be readily 

 followed by the polariscope therefore. 



As to the distribution of this enzyme in nature there is still 

 some dispute. According to some authors lactase is not pres- 

 ent in the gastric juice or in the pancreatic secretion, but other 

 investigators have reported finding it in both secretions. It 

 was formerly held that the disappearance of milk sugar in the 

 body is due largely to bacterial actions, as some of these organ- 

 isms are able to secrete an enzyme which acts on the sugar. 



