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- 
fication of esters, become stationary at a determinate point when a fixed 
proportion of hydration has taken place ; 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. 
jSTasse 5 stated that the sugar formed by the action of saliva is not 
dextrose, but another sugar of different reducing pow r er, 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 bo ilin g with a dilute mineral acid, as well as 
by the observation of birotation in the solution after boiling, which 
could only be clue 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 Jourh. Physiol., Cambridge and London, 1890, vol. xi. p. 226. 
2 Ztschr. f. physiol. Chcm., Strassburg, 1878, Bd. ii. S. 187. 
3 Journ. Chem. Soc, London, 1872, vol. xxv. p. 579. 
4 Ann. de chim. ctphys., Paris, 1847, tome xxi. p. 178. 
5 Arch. f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 477 ; see also Seegen, Centralbl. f. d. 
nied. JFissensch., Berlin, 1876, S. 851. 
6 Ztschr. f. physiol. Chem., Strassburg, 1877, Bd. i. S. 395 ; 1878, Bd. ii. S. 403. See 
also Brown and Heron, Proc. Roy. Soc. London, 1880, vol. xxx. p. 393. 
