ACTION OF PTYALIN. 433 



only inhibited because saliva made inactive in this manner can be react- 

 ivated by a small quantity of saliva or pancreatic juice. The experi- 

 ments recorded in support of this assumption are not conclusive enough 

 for such a view. That boiled starch (paste) is quickly, and unboiled 

 starch only slowly, converted into sugar is also of interest. Various 

 kinds of unboiled starch are converted with different degrees of rapidity. 

 Several series of investigations have been made upon the velocity 

 with which ptyalin acts, and as in testing enzyme action in general, the 

 experimenters have not made use of the different times required to pro- 

 duce equal chemical changes as a measure of the velocity, but have 

 taken the quantities of substance changed in equal times. Although 

 the results are somewhat divergent it is possible to deduce the following 

 from them. The velocity increases, at least under conditions otherwise 

 favorable, with the amount of enzyme and with an increasing temperature 

 to a little above 40 C. Foreign substances, such as metallic salts, 1 have 

 different effects. Certain salts, even in small quantities, completely arrest 

 the action; for example, HgCl 2 accomplishes this result completely by 

 the presence of only 0.05 p. m. Others have an accelerating action, and 

 this seems to apply to the salts of the saliva. According to GUYENOT 

 the saliva has a weaker action the more it is freed from salts by dialysis. 

 On the addition of salts the dialyzed saliva becomes active again, espe- 

 cially on the addition of calcium or potassium chloride. ROGER 2 be- 

 lieves that the presence of phosphates is a necessity for the action 

 of saliva. The amount of salts added is of special importance for the 

 action of the saliva, and one salt, which in small quantities has an accel- 

 erting action, may in large quantities have a retarding action. As an 

 example we can mention MgSO 4 , but unfortunately the opinions in 

 regard to this salt, as well as others, are widely divergent. The 

 presence of peptone has an accelerating action on the sugar formation 

 (CHITTENDEN and SMITH and others) . The accumulation of the products 

 of the amylolytic decomposition also checks the action of the saliva. 

 This has been show r n by special experiments made by SH. LEA. S He 

 made parallel experiments with digestions in test-tubes and in dialyzers, 

 and found on the removal of the products of the amylolytic decomposition 

 by dialysis that the formation of sugar took place sooner, but also that 

 considerably more maltose and less dextrin were formed. 



To show the action of saliva or ptyalin on starch the three ordinary 

 tests for dextrose may be used, namely, MOORE'S or TROMMER'S test or 



1 See O. Nasse, Pfliiger's Arch., 11, and Chittenden and Painter, Yale College 

 Studies, 1, 1885, 52; Kiibel, Pfliiger's Arch., 76; Patten and Stiles, Amer. Journ. of 

 Physiol., 17. 



2 Guyenot, Compt. rend. soc. biol., 63; Roger, ibid., 65. 



3 Journ. of Physiol., 11. 



