44 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



mercuric chloride. What is the result? For what substance 

 are these tests? > 



PTYALIN. 



This substance belongs to the class of amylolytic enzymes 

 in that its function consists in the conversion of starch and 

 glycogen into maltose. Its action is maximum at 46 C. 

 and is destroyed at 65-70 C. Alkalies and free acids tend 

 to retard its activity. Apparently it acts best in a neutral 

 solution and in the presence of proteins with which the 

 acids or alkalies may combine; in this way a greater degree 

 of acidity or of alkalinity may be borne without injury 

 than in a pure solvent. This is important to -remember 

 when considering the possibility of the continuance of saliva 

 digestion in the stomach. 



AMYLOLYSIS. 



The amylolytic action of ptyalin on starch is a hydrolytic 

 change in which successive products are evolved until the 

 final stage .of maltose or isomaltose is reached. The end 

 product of a similar cleavage by means of weak acids is 

 dextrose. Thus from starch is formed successively soluble 

 starch or amygdulin, then erythrodextrin, the achroodextrins, 

 maltodextrin and maltose, and, in case of acids, dextrose. 

 There are indications that at each step of the cleavage small 

 quantities of maltose are produced. These facts can be 

 shown by the following experiment: 



(a) Prepare some starch paste and allow it to cool to 

 40 C. Dilute the saliva five times and regulate the water- 

 bath for 40 C. Take 15 c.c of the paste; add to it 1 c.c. of 

 the diluted saliva and place the test-tube in the water-bath. 

 Watch the mixture until the turbidity disappears and the 

 solution becomes transparent. Then pour out into a clean 



