394 CHEMISTRY OF THE DIGESTIVE PROCESSES. 



Still later, Sheridan Lea, 1 working with much more dilute solutions than 

 were usually employed by other experimenters (0'4 to 4 per cent.), found as 

 much as 85 per cent, of the starch converted into sugar ; and by more closely 

 approximating the conditions of experiment to those of natural digestion, by 

 carrying out the experiment in a dialyser instead of in a glass vessel, obtained 

 a still greater reduction in the percentage of dextrin formed (7 to 8 per cent.). 

 He is therefore of the opinion that in the alimentary canal starch is 

 completely converted into sugar before absorption. The increase in sugar 

 formation, due to removal of the products of digestion, was more marked in 

 working with strong than in working with dilute solutions ; this also goes to 

 show that it is the accumulation of maltose in the solution which slackens and 

 stops the reaction. All chemical reactions involving hydration, such as saponi- 

 fieation of esters, become stationary at a determinate point when a lixed 

 proportion of hydration has taken plae ; and this point is rigorously de- 

 termined by the concentration in the solution of the various factors in the 

 reaction. If the substance or substances formed in the reaction be continuously 

 removed from the solution, or changed in nature as they are formed, the 

 reaction proceeds to completion ; but if the products of the reaction remain in 

 solution unchanged, at a perfectly fixed point, dependent on the concentration 

 in solution of each of the reacting substances, equilibrium is established, and 

 no further change in the composition of the solution takes place. 



On the other hand, Musculus and Gruber 2 claim to have isolated a dextrin 

 after acting on starch paste with diastase for five days, by precipitating the 

 dextrin with alcohol ; on this dextrin, diastase, even in the absence of the sugar ^ 

 has no further action. 



In 1872, O'Sullivan 3 rediscovered the sugar described by Dubrunfaut 4 

 as formed by the action of malt extract on starch paste, isolated it, 

 investigated its properties, and named it maltose. When it was so shown 

 that the sugar formed by the action of malt diastase is not grape-sugar, 

 attention was directed naturally to the sugars similarly formed by the 

 action of the digestive enzymes of the saliva and pancreatic juice. 

 Nasse 5 stated that the sugar formed by the action of saliva is not 

 dextrose, but another sugar of different reducing power, to which he 

 gave the name of ptyalose, which, however, was not maltose, as its 

 reducing power was doubled on boiling with acids, while that of maltose 

 was only increased by one -half. Soon after, v. Mering and Musculus 6 

 conclusively showed that the sugar really formed both by ptyalin and 

 amylopsin is identical with O'Sullivan's maltose, and these results have 

 been abundantly confirmed by subsequent observers. This result they 

 established by the amount of increase of reducing power and reduction 

 of rotating power, following boiling with a dilute mineral acid, as well as 

 by the observation of birotation in the solution after boiling, which 

 could only be due to the formation of grape-sugar. Such an analysis is 

 rendered easy by the widely different specific rotatory powers and 

 reducing powers of the two sugars (see table, p. 396). 



The action of malt diastase, ptyalin, or amylopsin on starch paste 

 takes place in several stages, corresponding to which more or less 



1 Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 226. 



2 Ztschr.f. physiol. Chem., Strasslmrg, 1878, Bd. ii. S. 187. 



3 Journ. Chem. Soc., London, 1872, vol. xxv. p. 579. 



4 Ann. de chim. etphys., Paris, 1847, tome xxi. p. 178. 



5 Arch. f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 477 ; see also Seegen, Centralbl. f. d. 

 med. PTissensch., Berlin, 1876, 8. 851. 



6 Zischr. f. physiol. Chem., Strassbnrg, 1877, Bd. i. S. 395 ; 1878, Bd. ii. S. 403. See 

 also Brown and Heron, Proc. Roy. 8oc. London, 1880,- vol. xxx. p. 393. 



