DIGESTION OF CARBOHYDRA TES. 393 



DIGESTION OF CARBOHYDKATES. 



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 dextrins : these are called amylolytic or diastatic 

 ferments. 2. Those which act on various saccharoses, producing glu- 

 coses : these are called inverting ferments. 



The two chief amylolytic 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 ; this 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 be 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 Musculus, 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. ges. NaturL, Niirnberg, 1831. 



2 Compt. rend. Acad. d. sc., Paris, 1845, tome xx. p. 1085. 



3 Journ. depharm. et chim., Paris, 1860, Ser. 3, tome xxxvii. p. 419. 



4 Payen, Chem. Centr.-BL, Leipzig, 1865, S. 845; Schwarzer, ibid., 1870, S. 295; 

 Schulze u. Marker, ibid., 1872, S. 823. 



