FUNCTIONS OF THE INTESTINAL JUICE. 189 



with the turbid fluid chyme causes it to change to a soft, cheesy, 

 granular mass, the appearance of which depends chiefly on the 

 precipitation and shrinking of the parapeptone and peptones. The 

 pepsin is rendered powerless, both it and the bile salts being car- 

 ried down with the precipitate. Gastric digestion is thus arrested 

 and the onward flow of the fluid chyme checked. As the alkaline, 

 pancreatic and intestinal juices meet this semi-fluid, cheesy mass, 

 the conversion of starch into sugar proceeds rapidly, even the raw 

 starch granules being thus changed. The small oil globules come 

 in contact with the alkaline mixture of bile and pancreatic juice. 

 The pancreatic secretion splits up some of the fat separating the 

 fatty acid from the glycerin radicle. Some of the soda of the 

 bile salt is substituted for the latter, and uniting with the fatty 

 acid forms a soap. In such a mixture as this an alkaline fluid 

 with proteid and soap in solution a fine emulsion is readily 

 formed, as can be seen by adding sodium carbonate to some rancid 

 oil. The free acid (the cause of rancidity in the oil) unites with 

 some soda to form a soap which in the alkaline mixture enables 

 the oil to be converted into an emulsion by even slight agitation, 

 so that the pancreas, by setting free fatty acid, and the bile pos- 

 sibly by contributing some soda, aid one another in giving rise to 

 a definite but small amount of soap. 



The precipitated parapetone and peptone and the finely divided 

 proteid are presented to the pancreatic juice in a form which it 

 can most easily attack, and thus the conversion of proteid into 

 peptones goes on rapidly. 



How far the peculiar action of trypsin on proteids, converting 

 them further into leucin and tyrosin, goes on in normal digestion 

 is not known, but it is probable that the production of these bodies 

 is increased with the over-abundant ingestion of proteid or a purely 

 meat diet, and is then useful as a means of preventing the inju- 

 rious effects of too great proteid absorption. 



The gastric chyme is therefore completely changed in the duo- 

 denum, and in the other parts of the small intestines we find in 

 its stead a thin creamy fluid which clings to the mucous mem- 

 brane, coats over its folds (valvulse conniventes) and surrounds 

 the long villi of the jejunum, etc. This intestinal chyme is the 



