THE SMALL INTESTINE 95 



still able to digest proteins, pepsin beginning the digestion 

 and carrying it to a stage at which the products are suscep- 

 tible to the action of erepsin. The presence of enteroki- 

 nase in the intestinal juice has just been noted. 



The Bile. The secretion of the liver cannot be regarded 

 in the same light as the digestive juices mentioned hereto- 

 fore. It is not secreted merely after meals, but is always 

 flowing through the ducts which converge from the several 

 lobes of the liver. It is not necessarily entering the in- 

 testine at all times, since the gall-bladder provides a place 

 for its temporary storage, as described in Chapter VI. 

 While the production of bile never ceases, it does show an 

 acceleration during the digestive periods, and this is be- 

 lieved to be in response to the stimulating effect of secretin. 



Bile attracted the attention of physicians in very early 

 times, its bright color and intensely bitter taste giving it 

 a certain distinction. It entered largely into ancient 

 theories of disease and of medicine. We have traces of 

 these facts in the root-meaning of such words as bilious, 

 choleric, and melancholy. In popular estimation bile is 

 a poison arising now and then in the system and causing 

 digestive disturbances. Patient study has shown that the 

 bile is a complex mixture, and that it numbers among its 

 constituents some which are waste-products and others 

 which have a favorable effect upon the progress of diges- 

 tion and absorption. It stands, therefore, in a position 

 intermediate between that of the gastric juice, which is 

 formed solely to advance digestion, and that of the urine, 

 which is composed of material useless to the body. 



The pigments of the bile are counted as waste substances. 

 A red one predominates in carnivorous animals. The bile 

 of the herbivora is green, as is also the case with human bile. 

 These pigments show in their chemical nature a close rela- 

 tionship with the red coloring-matter of the blood, the 

 important compound hemoglobin. All the evidence goes 

 to show that the bile-pigments are modified fractions of the 

 great hemoglobin molecule, and that their abundance is 

 an indication of the amount of destruction suffered by the 

 red corpuscles of the blood. These pigments are relatively 



