136 NUTRITION AND METABOLISM. 



which indicates at the same time that one cellulose, molecule gives many 

 sugar molecules. 



Cellulase is an enzyme which is quite difficult to obtain. Though it 

 must be produced by all the cellulose destroying molds and bacteria, 

 experiments have failed in some instances to prove its presence. It is 

 found in some wood destroying fungi and in some of the bacteria causing 

 the rot of vegetables. The organisms of certain plant diseases force their 

 way into the cell by dissolving the cellulose membrane by an enzyme, 

 while certain molds are able to puncture the cell wall mechanically. 



Diastase, or amylase, is the starch-dissolving enzyme which is one of 

 the most common enzymes in nature. It is found in all green plants, and 

 it forms during the sprouting of starchy seeds. Many molds and a few 

 bacteria produce this enzyme, while yeasts generally cannot decompose 

 starch for lack of diastase. Starch has the same formula as cellulose, and 

 it is broken up into soluble sugars in the same way. Much attention has 

 been paid to this process by the chemists, and it is found that the process 

 is a gradual one, giving first dextrins, and finally maltose (C^H^On). 

 The hydrolysis of starch expressed in chemical symbols may be presented 

 as follows: 



2 (C 6 H 10 5 ) n + nH 2 = nC 12 H 22 n 



Starch Maltose 



The disaccharides or double sugars, having the chemical formula 

 C 12 H 22 O U are broken up into single sugars, monosaccharides, by the 

 following process: 



C 12 H 22 U + H 2 0= C 6 H 12 6 + C 6 H 12 6 



The two molecules of C 6 H 12 O 6 are different with different sugars. If 

 the disaccharide is saccharose, the two monosaccharide molecules are 

 dextrose and levulose. Lactose will yield dextrose and galactose, and 

 maltose will give two molecules of dextrose. For each of these sugars, 

 there is a special enzyme which can hydrolyze only its particular sugar and 

 none of the others; like a key, made for one lock, it will not open another 

 lock. Maltase will split only maltose molecules, not lactose, while the 

 lactase cannot attack the maltose. Invertase (or sucrase) will decompose 

 nothing but saccharose. This decomposition of the complex sugars into 

 the simple sugars is necessary because only sugars of the type C 6 H 12 O 8 

 can be fermented directly by the fermenting enzyme in the cell, be it an 

 alcoholic or lactic or gassy fermentation. This explains why beer yeast 



