ENZYMES. FERMENTATION 401 



5 c.c. of starch solution, I c.c. of dilute acetic acid (0-5 per cent.) 

 and 5 c.c. of saliva solution are placed in a third test tube. 



5 c.c. of starch solution, i c.c. of dilute alkali (-iN or 0-4 per 

 cent.) and 5 c.c. of saliva solution are placed in a fourth test tube. 



5 c.c. of starch solution, I c.c. of sodium chloride solution (i per 

 cent.) and 5 c.c. of saliva solution are placed in a fifth test tube. 



The five tubes are placed in the water-bath at 40 and at inter- 

 vals drops from each are tested with iodine solution. 



Hydrochloric acid completely stops the action of diastase ; acetic 

 acid hinder* the action, i.e. the conversion of starch into achroodextrin 

 and maltose takes longer ; alkali may hasten, but if strong will stop 

 the action. A small concentration of sodium chloride hastens the 

 action ; sodium chloride of a concentration of 5 per cent, will binder 

 the action. 



II. Invertase. 



The best source of invertase is yeast from which it may be prepared by 

 several methods. Method of Autolysis. It is most conveniently prepared by. 

 grinding 500 gm. yeast with 30 gm. of calcium carbonate into a thick paste and 

 placing the paste in a wide- mouthed bottle. 25 c.c. of chloroform are added 

 and it is kept for 3-4 days in a warm room. The solution is filtered from 

 the insoluble matter and treated with an equal volume of alcohol. The pre- 

 cipitate is washed with alcohol and ether and dried in vacua over sulphuric acid. 



A 'I -i per cent, solution of the preparation is used to demon- 

 strate the action of invertase. The autolysed yeast, if diluted about loo 

 times with water, also serves for showing the presence of invertase. 



A cane-sugar solution of I per cent, is prepared as substrate ; 5 c.c. 

 of the invertase solution are added to 5 or 10 c.c. of the cane sugar 

 solution ; at the same time 5 c.c. of boiled invertase solution are 

 added to another 5 c.c. of cane sugar solution to act as a control. 



The solutions may be kept for about 5 minutes at room tempera- 

 ture or at 40. They are tested with Fehling's solution. Reduction 

 only occurs in the first tube due to the formation of glucose and 

 fructose. 



Demonstration of Invertase in the Succus Entericus or Intestinal 

 Mucous Membrane. 



The succus entericus, or an extract of the cells of the mucous 

 membrane of the small intestine, prepared by grinding the material 

 with sand, allowing it to stand with water for 1 2 hours in the presence 

 of toluene and straining through muslin, is divided into two equal 

 portions. One portion is boiled and cooled. To each portion is 

 added an equal volume of I per cent, cane sugar solution. I per 

 cent, of toluene is added to each and the two mixtures are kept at 37 

 for 12-24 hours. Each solution is tested with Fehling's solution. 

 Reduction only occurs where the unboiled extract is present showing 

 the presence of invertase. 



