308 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Intestinal Secretion. — The small intestine is lined with tubular glands, 

 the crypts of Lieberkiihn, that are supposed to form a secretion of consid- 

 erable importance in digestion. To obtain the intestinal secretion, or suceus 

 enterims, as it is often called, recourse lias been had to an ingenious operation 

 for establishing a permanent intestinal fistula. This operation, which usually 

 goes under the name of the " Thhy-Vella fistula," consists in cutting out a 

 small portion of the intestine without injuring its supply of blood-vessels or 

 nerves, and then sewing the two open ends of this piece into the abdominal 

 wall so as to form a double fistula. The continuity of the intestines is estab- 

 lished by suture, while the isolated loop with its two openings to the exterior 

 can lie used for collecting the intestinal secretion uncontaminated by partially- 

 digested food. The secretion is always small in quantity, and it must be 

 started by a stimulus of some kind. According to Rohmann, 1 it varies in 

 quantity in different parts of the small intestine, being very scanty in the upper 

 part and more abundant in the lower. The intestinal secretion is a yellowish 

 liquid with a strong alkaline reaction. The reaction is due to the presence of 

 sodium carbonate, the quantity of which is about 0.25 to 0.50 per cent. The 

 chemical composition of the secretion has not been satisfactorily determined, 

 but its digestive action has been investigated with success. Upon proteids and 

 fats it is said to have no specific action — that is, it contains neither a proteolytic 

 nor a fat-splitting enzyme. The possible value of its sodium carbonate in aiding 

 the emulsification of fats has been referred to in the preceding paragraph. 

 Upon carbohydrates the secretion has an important action. In the first place, 

 it has been shown that it contains an amylolvtic enzyme that is more abun- 

 dant in the upper than in the lower part of the intestine. This enzyme doubt- 

 less aids the amylopsin of the pancreatic secretion in converting starches to 

 sugar (maltose) or sugar and dextrin. What is still more important, however, 

 is the presence of inverting enzymes (invertase) capable of converting cane- 

 sugar (saccharose) into dextrose and levulose, and of a similar enzyme (mal- 

 tase) capable of changing maltose to dextrose. Both of these effects are 

 examples of the conversion of di-saccharides to niono-saecharides. 



The di-saccharides of importance in digestion are cane-sugar, milk-sugar, 

 and maltose. The first of these forms a common constituent of our daily diet; 

 the second occurs always in milk ; and the third, as we have seen, is the main 

 end-product of the digestion of starches. These substances are all readily 

 Boluble, and we might expect that they would be absorbed directly into the 

 blood without undergoing further change. As a matter of fact, however, it 

 seems that they are first dissociated under the influence of the sugar-splitting 

 enzymes into simpler mono-saccharide compounds, although in the case of 

 lactose this statement is perhaps not entirely justified, our knowledge of the 

 fate of this sugar during absorption being as yet incomplete. According 

 to some authors, lactose is absorbed unchanged (sec Chemical section), 

 'flic general nature of this change is expressed in the three following 

 reaction- : 



1 /'///(•/./■'.< Arehiv fur die gesammte Physiologie, 1887, l>d. 41,8.411. 



