CHEMISTRY OF DIGEST I OX AND NUTRITION. 305 



starch quickly disappears and maltose or maltose and dextrin are found 

 in its place. Amylopsin shows the general reactions of enzymes with rela- 

 tion to temperature, incompleteness of action, etc. Its specific reaction is its 

 effect upon starches. Investigation has shown that the changes caused by it 

 in the starches are apparently the same as those produced by ptyalin. In 

 fact, the two enzymes ptyalin and amylopsin are identical in properties as 

 far as our knowledge goes, so that it is not uncommon, in German liter- 

 ature especially, to have them both described under the name of ptyalin. 

 The term amylopsin is convenient, however, in any case, to designate the 

 special origin of the pancreatic enzyme. As to the details of its action, it is 

 unnecessary to repeat what has been said on page 285. The end-products 

 of its action, as far as can be determined from artificial digestions, are a sugar, 

 maltose (C^H^Oj^H^O), and more or less of the intermediate achroodextrins, 

 the relative amounts depending upon the completeness of digestion. As has 

 previously been said, there are indications that under the favorable conditions 

 of natural digestion all the starch may be changed to maltose, but possibly 

 it is not necessary that the action should be so complete in order that the 

 carbohydrate may be absorbed into the blood, as will be shown when we come 

 to speak of the further action of the intestinal secretion upon maltose and the 

 dextrins. The amylolytic action of the pancreatic juice is extremely import- 

 ant. The starches constitute a large part of our ordinary diet. The action of 

 the saliva upon them is probably, for reasons already given, of subordinate 

 importance. Their digestion takes place, therefore, entirely or almost entirely 

 in the small intestine, and mainly by virtue of the action of the amylopsin 

 contained in the pancreatic secretion. The action of the amylopsin is supple- 

 mented to some extent, apparently, by a similar enzyme formed in small 

 quantities in the intestinal wall itself, the nature of which will be described 

 presently in connection with intestinal secretion. 



Steapsin. — Stcapsin, or lipase, is the name given to a fat-splitting enzyme 

 occurring in the pancreatic juice. It is of the greatest importance in the 

 digestion and absorption of fats. The peculiar power of the pancreatic juice 

 to >plit neutral fats with the liberation of free fatty acid was first described 

 by Bernard. His discovery has since been corroborated for different animals, 

 including man, by the use of normal pancreatic juice obtained from a fistula, 

 or by the aid of the tissue of the fresh gland, or, finally, by means of extracts 

 of the gland. When neutral fats (see Chemical section for the composition 

 of fats) are treated with an extract containing steapsin, they take up water 

 and then undergo cleavage (hydrolysis), with the production of glycerin and 

 the free fatty acid found in the particular fat used. This reaction is explained 

 by the following equation, in which a general formula for l'ats is used: 



(:,H 5 (C n II 2n+1 COO) 3 + 3H z O = C 3 H,(()I I), + 3(CJ I,.,, , ,< !< )OII). 



Fat. Glycerin. Free fatty acid. 



The reaction in the case of palmitin would be — 



C 8 H 6 (C I6 H 31 COO) s + 3H 2 = C,H 8 (OH) s + 3(C u H 81 COOH) 



Palmitin. Glycerin. Palmitic acid. 



Vol. I.— 20 



