THE CHEMISTRY OF DIGESTION 997 



has no definite influence of this kind. In other words, the fact that it 

 diminishes putrefaction in the intestine, is due chiefly to its power of 

 hastening the absorption of those substances which are most likely 

 to give rise to these processes. Bile is to a certain extent fexcretory. 

 In addition, it aids in neutralizing the acid chyme and in precipitat- 

 ing its unpeptonized protein. This renders the chyme more viscid 

 and retards its progress through the intestine, thereby augmenting 

 absorption. 



The Function of the Intestinal Juice. — The principal action of the 

 intestinal secretion is exerted upon the carbohydrates. Its invertase 

 changes cane-sugar into glucose and levulose or fructose, whereas its 

 maltase^ transforms maltose into glucose. ^ A special enzyme, called 

 lactase, 3 is abundantly present in young animals for the purpose of 

 converting milk-sugar into galactose and glucose. The ferment 

 enterokinase (Pawlow) which activates trypsinogen, is widely distrib- 

 uted through the intestine. A similar body is erepsin^ which increases 

 the hydrolysis of the first products of the proteolysis and rapidly changes 

 albumoses and peptones into amino- and diamino-acids. Moreover, 

 since a great deal of fat may be split up in the small intestine 

 even in the absence of both bile and pancreatic juice, it is assumed that 

 it contains a lipase of relatively feeble power. The sodium carbonate, 

 in which it is rather rich, must, of course, aid in the formation of soaps 

 from the fatty acids. 



This fact brings up the important point that the secretions in the 

 intestine form a suitable medium for the growth of bacteria, contrary 

 to the gastric juice which by virtue of its acidity attenuates micro- 

 organisms. Some of them, however, reach the intestine in spite of 

 the gastric juice and produce here certain enzymes, the actions of 

 which are very similar to those of the ferments normally contained 

 in the local secretions. In some instances, these putrefactive organ- 

 isms also give rise to more specific reactions, as follows: 



(a) On Carbohydrates. — The most important reaction is the lactic acid fermenta- 

 tion which is chiefly responsible for the formation of intestinal gases. It usually 

 takes place in two stages which may be represented by the following two equations : 



CizHazOn + H2O = 4C3H6O3 

 (Lactose) (Lactic acid) 



4C3H6O3 = 2C4H8O2 + 4CO2 + 4H2 

 (Lactic acid) (Butyric acid) 



Vegetable food increases this fermentation, the cellulose being split into carbonic 

 acid and urethane. 



(6) On Fats. — Some bacteria possess a lipolytic action and are capable of pro- 

 ducing lower acids, such as valeric and butyric. It cannot surprise us, therefoi^, 



1 Rosenbloom, Conn. Biolog. Chem., xiv, 1913, 241, and Hammarsten, 

 Ergebn. der Physiol., 1905. 



2 Rohmann, Pfliiger's Archiv, xH, 1887, 424. 



3 Halliburton, Textb. of Chem. Path, and Physiol., 1891. 



^ Cohnhein, Zeitschr. fiir phys. Chemie, xxxvi, 1902, 13, and Vernon, Jour, of 

 Physiol, xxxii, 1904, 32. 



