76 THE ACTION OF ENZYMES 



apparently with the formation of sugars by an enzyme 

 named cytase, and a cellulose - dissolving enzyme is 

 possessed by many fungi, both parasitic and sapro- 

 phytic, which enables them to penetrate the epidermis, 

 wood and other tissues of plants. 



In a later chapter (Chap. XIV.) is discussed the fermen- 

 tative decomposition of the cellulose of leaves, stems, straw, 

 paper, and similar materials by means of certain species 

 of bacteria present in manure heaps, the mud of swamps, 

 and the intestinal tract of certain herbivorous animals. 



(ii) Disaccharoses. The disaccharoses have the 

 formula C 12 H 8 2O n . Three of the best known repre- 

 sentatives are cane-sugar, milk-sugar, and malt-sugar. 



(a) Cane-sugar or Saccharose is a very sweet crystalline 

 carhohydrate found in abundance in the cell sap of the 

 sugar cane, beetroot, and other plants. 



When boiled with dilute acids it is transformed into 

 grape-sugar and fruit-sugar, the mixture of these two 

 being sometimes spoken of as invert-sugar. 



An inverting enzyme, invertase, which effects a similar 

 chemical change in cane-sugar, is widely distributed in 

 nature : it is met with in yeast, and is possessed by Bs. 

 megatherium, Bs. vulgatus, and other bacteria. 



Cane-sugar does not reduce Fehling's solution, and 

 cannot be fermented directly by yeast. 



Ex. 42. Dissolve some ordinary sugar in water and 



(i) Test some of the solution for a " reducing " sugar as in 



Ex. 44. 



(ii) Take 10 c.c. of the solution and add to it three or four 



drops of strong hydrochloric acid : boil for twenty minutes, and 



after neutralizing the acid with a solution of sodium carbonate, 



boil and test again with Fehling's solution. 



