182 MANUAL OF PHYSIOLOGY. 



alimentary tract are numerous ; a short review may therefore be 

 useful. 



When the acid gastric chyme flows into the duodenum, a flow 

 of bile takes place from the gall-bladder, and at the same time 

 the secretions of the pancreas, Bru'nner's glands, and Lieberkiihn's 

 follicles are poured copiously into the intestine. The bile meeting 

 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 parapetone 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 parapetoue 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 ty rosin, 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 



