146 PHYSIOLOGICAL CHEMISTRY. 



with ptyalin the main action seems to end with the produc- 

 tion of maltose; at all events no large amount of the hexose 

 sugar is formed. A little maltase is said to be present. Fur- 

 thermore the whole of the starch is not brought into the sugar 

 condition ; a portion remains in the form of a dextrin. In an 

 earlier chapter something was said about the character of these 

 dextrins. 



In most respects the behavior of ptyalin is very similar to 

 that of malt diastase, which can be shown by a simple experi- 

 ment with commercial malt. This substance is usually made 

 by germinating barley and permitting the growth to continue 

 some days, the barley in moist condition being spread out on 

 a so-called malting floor to encourage the growth and prevent 

 overheating. In the germination the enzyme is developed, 

 probably from a portion of the protein substance present. 

 When the action has gone far enough, which the malster rec- 

 ognizes by the appearance of the rootlet thrown out, the action 

 is checked by quick drying, leaving the diastase in permanent 

 stable condition. This malt is made in enormous quantities 

 for use in breweries and distilleries. In the germinating seed 

 in the ground the same enzyme is formed which converts 

 starch into soluble food for the young plant. 



Ex. Mix about 10 gm. of pale ground malt with 50 cc. of lukewarm 

 water, and allow the mixture to stand a short time, with frequent stirring 

 and shaking. Then filter and add the clear, bright filtrate to a thin starch 

 paste made of 10 grams of starch with 250 cc. of water. The starch paste 

 must be cool when the malt extract is added. Place the mixture on the 

 water-bath and warm to 5o-6o C, and maintain this temperature. Note 

 that the liquid gradually becomes thin and transparent. From time to time 

 remove a few drops by means of a pipette, and test with iodine solution. 

 At first a deep blue color appears, but this grows weaker, giving place to 

 violet, then to yellowish brown and finally no color is obtained, indicating 

 completion of the reaction. The starch paste is first converted into dex- 

 trin and finally into maltose. Evaporate the solution to a very small 

 volume and observe the taste and appearance of the residue. In the end 

 product there is usually about 80 per cent of maltose and 20 per cent of 

 dextrin when made at the temperature of this experiment. 



It has been found in practice that the amount of malt sugar 

 formed depends on the temperature and duration of the diges- 



