DIGESTION OF CARBOHYDRA TES. 393 
DIGESTION OF CARBOHYDRATES. 
The digestion of carbohydrates is brought about by the action of two 
distinct classes of enzymes, namely — 1. Those which act on starches, 
producing sugars and dextrine: these are called amylolytic or diastatic 
ferments. 2. Those which act on various saccharoses, producing glu- 
coses: these are called inverting ferment-. 
The two chief amyl. .lytic ferments found in the digestive juices are 
ptyalin and amylopsin. "'The action of these ferments on starch may be 
demonstrated by adding to starch paste, either saliva or pancreatic juice, 
or a watery infusion of salivary or pancreatic gland. The paste very 
soon becomes quite fluid, and if the fluid be tested chemically for starch, 
it will be found that this substance is rapidly disappearing, and that a 
reducing material is being formed in continuously increasing amount in 
the solution. This testing may be done by removing a drop of the 
solution at intervals, and mixing it with a drop of a solution of iodine. 
At first the deep blue colour given by starch is obtained ; tins is replaced 
after a time by a violet, this again by a red colour, and finally no 
coloration at all is obtained. If at each of these stages portions of the 
solution lie tested with Fehling's solution, it will be found that it has 
acquired reducing power, and that the amount of reduction increases 
with the length of time during which the action goes on. 
The diastase of malt is very similar in its action to both these 
ferments, but is not identical with either of them, as is shown by the 
fact that while ptyalin and amylopsin act best at body temperature, the 
optimum temperature for the action of malt diastase is about 55° C. 
Products of digestion of starch. — Whether the ferments are 
identical or not, their action, according to all observers, is the same. It 
was shown by Leube, 1 in 1831, that saliva dissolves starch-paste and 
forms sugar, and the same was shown for pancreatic juice by Bouchardat 
and Sandras, 2 in 1845. It was for many years believed that the 
action of these ferments was closely analogous to that of mineral 
acids, and that the sugar produced was grape-sugar. Dextrin was 
supposed to be the first stage in the process of saccharification, and 
from the dextrin it was thought that grape-sugar was afterwards 
formed. Musculus 3 was the first to show that all the starch was not 
so converted into sugar, but that saccharification only proceeded until 
the solution gave no longer a colour reaction with iodine : on adding 
fresh starch-paste, the reaction recommenced and proceeded as before, 
until again all colour reaction with iodine had vanished, when, as 
before, the reaction slackened and stopped, although there remained 
plenty of dextrin in the solution. 
According to the earlier work of Museums, the quantitative relationship in 
which the sugar and dextrin stand at the end of the reaction is, one part of 
sugar to two of dextrin ; his later papers gave the reaction as stationary, 
when approximately equal quantities of sugar and dextrin are present in the 
solution. 4 
1 Arch. f. d. rjes. Naturl., Xiiriiberg, 1831. 
2 Compt. rend. Acad. d. se., Paris, 1845, tome xx. p. 1085. 
3 Journ. de pharra. et chim., Paris, 1860. Ser. 3, tome xxxvii. p. 419. 
4 Paven. Litem. Gembr.-Bl., Leipzig, 1865, S. 845; Schwarzer, ibid., 1870, S. 295; 
Sclmlze'u. Marker, ibid., 1S72, S. 823. 
