THE BILE. 335 



expulsion 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 nutrition, but which would be 

 positively injurious if allowed to mingle with the general 

 mass of the blood. The liver, therefore, may be supposed 

 placed in the only road by which such matters can pass 

 into the general current, jealously to guard against their 

 further progress, and turn them back again into an 

 excretory channel. The frequency with which metallic 

 poisons are either excreted by the liver or intercepted and 

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

 may be adduced as evidence for the probable truth of this 

 supposition. 



Though the 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 more 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 



