DIGESTION. 285 



From the peculiar manner in which the liver is supplied with much 

 of the blood that flows through it, it is probable that this organ is excre- 

 tory, not only for such hydro-carbonaceous matters as may need expul- 

 sion from any portion of the blood, but that it serves for the direct 

 purification of the stream which, arriving by the portal vein, has just 

 gathered up various substances in its course through the digestive organs 

 substances which may need to be expelled, almost immediately after 

 their absorption. For it is easily conceivable that many things may be 

 taken up during digestion, which not only are unfit for purposes of nu- 

 trition, but which would be positively injurious if allowed to mingle 

 with the general mass of the blood. The liver, therefore, may be sup- 

 posed placed in the only road by which such matters can pass unchanged 

 into the general current, jealously to guard against their further pro- 

 gress, and turn them back again into an excretory channel. The fre- 

 quency with which metallic poisons are either excreted by the liver, or 

 intercepted and retained, often for a considerable time, in its own sub- 

 stance, may be adduced as evidence for the probable truth of this sup- 

 position. 



(2.) As a digestive fluid. Though one chief purpose of the secretion 

 of bile may thus appear to be the purification of the blood by ultimate ex- 

 cretion, 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 excretions are, but is made to pass into the in- 

 testinal 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 in- 

 testines much greater, during digestion than at any other time ; al- 

 though, 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 tempora- 

 rily (to be afterwards re-absorbed), or permanently. 



Eespecting the functions discharged by the bile in digestion, there is 

 little doubt that it (a.) 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 un- 

 affected, chyle was no longer well forme.d ; the contents of the lacteals 



