344 Chittenden and Stuith — Diastatic Action of Saliva. 



tatic action of ptyalin is dextrose ; the sugar intermediate between this 

 body and the de.vtrins, and which is formed in much larger quantity 

 is maltose, with a relative reducing power of 66 as compared with 

 dextrose, 100; while the achroodextrins and other intermediate pro- 

 ducts have very small reducing power ; consequently the reducing 

 power of a digestive mixture must necessarily express the relative 

 diastatic action of the ferment present, since increased action means 

 an increased formation of reducing bodies, of which the final product 

 has the highest reducing power. In this connection it is well to re- 

 member that diastase and ptyalin both convert only a limited quan- 

 tity of starch into sugar or reducing bodies,* and that no matter how 

 great the excess of ferment or the length of time the action is con- 

 tinued, the percentage of starch changed into sugar does not ordi- 

 narily exceed 53 per cent.f The general method employed in our 

 work for testing the diastatic action of saliva was as follows : the 

 volume of the digestive mixture was in every instance 100 c.c. ; 

 the amount of starch| present, 1 or 2 grams, previously boiled in 

 a definite amount of water ; the temperature of digestion 38-40° C. ; 

 the length of time generally 30 minutes. When the digestion was 

 finished, diastatic action was at once stopped by boiling the mix- 

 ture ; when cold, the mixture was diluted with distilled water to 

 200 c.c. and filtered ; 25 c.c. of the filtrate or ^th of the entire 

 fluid was then precipitated with Fehling's solution according to 

 Allihn's§ data and method ; the reduced copper was filtered through 

 an asbestos filter in a small weighed glass tube and ignited directly 

 in a current of hydrogen gas and weighed as metallic copper. 

 By means of Allihn's tables of reduction equivalents the correspond- 

 ing amount of sugar, calculated as dextrose, is easily obtained, 

 from which the percentage amount of starch converted into reducing 

 bodies can be computed, calling dextrose 0^1,^0 j, and the 

 starch C H ^O^.l The following experiment illustrates the accuracy 

 of the method and the reliance which can be placed upon it; two 

 solutions of 100 c.c, each containing 2 grams of starch and 4 c.c. of 



* Schulze and Marker, Chem. Centralbl. 1872, 823. Chittenden and Ely, Amer. 

 Chem. Jour., iv, 120. 



+ Miisculus and v. Mering, Zeilschrift fiir Physiolog. Chem., ii, p. 415. 



I The starch was exactlj'^ neutral ; made so by long and thorough washing witli pure 

 water. § Loc. eit. 



II The actual amount of stiirch changed is, liowever, somewhat greater than would 

 appear by this eifuation, since, as has already been mentioned, considerable of the 

 sugar formed is mallose, which has only two-thirds the reducing power of dextrose. 



