342 STUDIES IN ADVANCED PHYSIOLOGY. 



Third: All the starches are finally changed into maltose 

 by the renewed action of the ptyalin of the saliva, but 

 mainly by that of the amylopsin ferment of the pancreas. 



Fourth: The fats have been doubly affected. A small 

 part has been saponified, that is, made into soap by the 

 steapsin, and the remainder has been emulsified. Sugars 

 have been left untouched. It will be seen, therefore, that 

 at this stage of digestion all the proteids, all the fats, all 

 the starches are ready for absorption. The sugars alone 

 have escaped any action. 



4. The Bile. The liver plays but a very small part in 

 the process of digestion, and the bile which it pours into 

 the duodenum must not be classed in importance along with 

 the digestive agents so far considered. The liver is an ex- 

 ceedingly important organ when the phenomena of nutri- 

 tion and metabolism in the body are considered, but plays 

 a minor role in digestion. In fact, bile is largely an excre- 

 tory product. It digests nothing itself, although incidentally 

 it does serve several digestive purposes. Human bile is of 

 a golden color, exceedingly bitter, neutral in its re-action, 

 and emitting a peculiar characteristic odor. It is a little 

 heavier than water. When the bile is taken from the gall- 

 bladder it contains a mucin-like substance which was added 

 to it in its passage through the bile-ducts and in its stay in 

 the gall-bladder. This was formerly designated as ordinary 

 mucin, but its re-actions are not those of ordinary mucin, 

 and it is probably a slightly different product. However, 

 in a general way we may still speak of it as mucin. While 

 the color is usually a golden yellow it changes its color so 

 readily as to appear sometimes a greenish yellow, some- 

 times a greenish brown, still other times pure green or 

 brown. These changes in color are brought about by dif- 

 ferent degrees of oxidation of the bile pigments. 



The quantity of bile secreted during a day for average 

 persons is from 600 to 900 cubic centimeters. In animals 

 which have no gall-bladder the bile is poured into the in- 

 testine in a continuous stream, but in those possessing a 



