72 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



With the other half of the solution try the Trommer's 

 sugar test. As a check repeat the same experiment with 

 boiled saliva: the fluid does not become clear, the starch 

 remains unchanged. 



2. Repeat experiment 1, but digest for an hour at 40, then 

 shake the solution obtained with some yeast, fill a fermenta- 

 tion-tube with it, and let stand at about 35 : the sugar, mal- 

 tose, formed in the salivary digestion is fermentable. 1 



Influence of Acids on the Diastatic Action of Ptyalin. 



(a) Shake together thoroughly 10 cc. of starch paste and 

 1 cc. of 0.27 per cent, hydrochloric acid (6 cc. of hydrochloric 

 acid, 1.19 sp. gr., diluted to one liter), add 1 cc. of saliva, and 

 digest on the water-bath at 40. The diastatic action of the 

 enzyme is completely prevented by the acid. 



(b) Repeat the experiment with 1 cc. of dilute acetic acid 

 of 0.5 to 1 per cent. (1 to 2 cc. of glacial acetic acid to 200 cc. 

 of water) : the diastatic action is not prevented, but it is per- 

 ceptibly retarded. An excellent arrangement of these ex- 

 periments is also the following: 2 



The mixtures of starch paste and saliva and in the given 

 case also the acid are placed in test-tubes in a water-bath 

 whose temperature is kept at 40 to 42. Each test-tube has 

 a pipette standing in it. From time to time a drop of the 

 mixture is taken out and brought into contact with a dilute 

 .solution of iodine in a solution of potassium iodide. For this 

 purpose place beforehand a number of drops of the iodine 

 solution at regular intervals (in rows) on a porcelain plate. 

 If we proceed in this manner, the addition of a drop of the 

 mixture to the iodine solution requires only the smallest 

 amount of time, so that the time interval which elapses 



1 The yeast contains maltase, which inverts the maltose. The glucose 

 formed then ferments with the yeast. O. 

 3 Virchow's Arch. 120, 343. 



