DETERMINATION OF ENZYMES 173 



3. Add freshly made solution of potassium ferrocyanide. Iron 

 gives a blue precipitate of ferric ferrocyanide. 



The residue from solution II, insoluble in HC1, should be 

 washed with water, then fused with excess of sodium carbo- 

 nate, dissolved in warm water and filtered. Concentrate the so- 

 lution and while stirring add hydrochloric acid slowly to excess. 

 If silicic acid is present a gelatinous precipitate is formed, which, 

 when evaporated to dryness, yields an insoluble white powder. 



241. Enzymes. A number of substances in the plant of unknown 

 composition have the power of producing hydrolytic cleavage in 

 various materials which are used for food, or constructive pur- 

 poses, and are known as the enzymes, or soluble ferments. They 

 are classified according to the character of the substances upon 

 which they act (See classification of enzymes). 



Soluble ferments are prepared from tissues in which they are 

 found by extraction with cold water, dilute glycerine, or dilute 

 saline solution. They are most readily obtained from tissues in 

 which large quantities of reserve food are being quickly digested 

 and translocated, as in the endosperms of germinating seeds. The 

 material for treatment should be finely divided and covered with 

 about twice its volume of the solvent. After standing for twenty- 

 four hours the extract should be drawn off, filtered, and alco- 

 hol (95 per-cent.) added to precipitate the enzyme. Other sub- 

 stances such as proteids, will be present in the extract and 

 will be precipitated with the enzymes. The precipitate should be 

 removed by filtering, and dried at low temperatures. The kind 

 of food present in the tissues in which the enzyme was found will 

 suggest the character of the ferment. 



242. Determination of Enzymes. The tissue to be extracted 

 should be ground finely and treated with twice its volume of water, 

 glycerine or salt solution for twenty-four hours, and the following 

 tests made : 



1. To 10 cc. of 1 per-cent. starch paste add 5 cc. of the ex- 

 tract. A clearing up of the starch mixture occurring after sev- 

 eral hours will indicate diastase. Draw off a little of the mixture 



