330 DIGESTION. 



retained, often for a considerable time, in its own substance, 

 may be adduced as evidence for the probable truth of this 

 supposition. 



Though one chief purpose of the secretion of bile may 

 thus appear to be the purification of the blood by ultimate 

 excretion, yet there are many reasons for believing that, 

 while it is in the intestines, it performs an important part in 

 the process of digestion. In nearly all animals, for example, 

 the bile is discharged, not through an excretory duct 

 communicating with the external surface or with a simple 

 reservoir, as most secretions are, but is made to pass into 

 the intestinal canal, so as to be mingled with the chyme 

 directly after it leaves the stomach ; an arrangement, the 

 constancy of which clearly indicates that the bile has some 

 important relations to the food with which it is thus mixed. 

 A similar indication is furnished also by the fact that the 

 secretion of bile is most active, and the quantity discharged 

 into the intestines much greater, during digestion than at 

 any other time ; although, without doubt, this activity of 

 secretion during digestion may, however, be in part 

 ascribed to the fact that a greater quantity of blood is sent 

 through the portal vein to the liver at this time, and that 

 this blood contains some of the materials of the food 

 absorbed from the stomach and intestines, which may need 

 to be excreted, either temporarily, to be re-absorbed, or 

 permanently. 



Respecting the functions discharged by the bile in 

 digestion, there is little doubt that it assists in emulsifying 

 the fatty portions of the food, and thus rendering them 

 capable of being absorbed by the lacteals. For it has 

 appeared in some experiments in which the common bile- 

 duct was tied, that although the process of digestion in the 

 stomach was unaffected, chyle was no longer well-formed ; 

 the contents of the lacteals consisting of clear, colourless 

 fluid, instead of being opaque and white, as they ordinarily 

 are, after feeding. (2.) It is probable, also, from the 



