ENZYMES. FERMENTATION 399 



DEMONSTRATION OF THE ACTION OF ENZYMES. 



Since enzymes can only be recognised by their action, their demon- 

 stration necessitates the knowledge of the chemical and physical pro- 

 perties of the compounds upon which they act ; e.g. starch and its 

 products maltose and dextrin, fats and their products glycerol and 

 fatty acids, proteins and their products the proteoses, peptones and 

 amino acids. Either the disappearance of substrate, or the appear- 

 ance of the products, or both, may be demonstrated. 



Frequently the amount of enzyme in a solution or in a preparation 

 is very small and a considerable time must be allowed before its action 

 can be demonstrated, e.g. from I day to 3 or 4 days. Under these con- 

 ditions an antiseptic, preferably I per cent of toluene or chloroform, 

 is added to prevent the action of bacteria. The antiseptics destroy 

 the bacteria or inhibit their growth ; they have no action on the 

 enzyme. 



I. Diastase or Amylase. 



(1) Malt Diastase. 



The chief source of diastase is malt. Malt is prepared by steeping barley 

 or other seeds of cereals in water and allowing them to germinate in a warm 

 place until the plumules have reached a length of about - inch. The sprouted 

 grain is dried and cured in a kiln. The composition of the grain alters under 

 these conditions : the amount of starch decreases, the amount of reducing 

 carbohydrates increases. Its colour is light to dark yellow. The seeds 

 should break easily, should have a white interior and a sweet flavour. Malt 

 should be free from broken and damaged seeds and the dried rootlets. 



Malt extract is prepared from the dried material by treatment with water ; 

 the aqueous solution may be evaporated to dryness. Its chief use is in 

 brewing, but it is used in medicine as a food for its high content in maltose 

 and for its diastatic action ; some varieties of malt extract contain no diastase 

 as they have been boiled. 



A i to 2 per cent, filtered extract serves for the demonstration of diastase. 



An active diastase is prepared by treating malt, or ground barley, with 

 2 to 4 parts of 20 per cent, alcohol, for 24 hours. The extract is precipitated 

 by adding not more than 2-J volumes of alcohol. The precipitate is rapidly 

 treated with absolute alcohol and ether and dried in vacuo. (Lintner.) 



(2) Pancreatic Diastase. 



A solution containing diastase can be prepared from the pancreas of 

 animals by allowing a fresh pancreas (free from fat), which has been finely 

 minced, to stand with twice its weight of glycerin, for 12 to 24 hours and 

 straining through muslin. Before use the solution may be diluted with i to 2 

 volumes of water or preferably i to 2 drops of the concentrated extract may 

 be used. Diastase is present in pancreatic juice and may be detected in -i to 

 i c.c. as described below. 



(3) Salivary Diastase. 



A solution of this diastase is prepared by rinsing out the mouth 

 two or three times with 20 c.c. of distilled water, warmed to 40, for 

 I to 2 minutes. The water is collected in a beaker and filtered 



A I to 2 per cent, solution of soluble starch or starch paste 

 solution is prepared as substrate. The presence of diastase is shown 

 by the disappearance of starch and the appearance of erythrodextrin, 

 achroodextrin and maltose ; thus : 



