DIGESTION. 279 



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. 



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

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

 excretion, yet tli3re 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 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 secre- 

 tion of bile is most active, and the quantity discharged into the intestines 

 much greater, during digestion than at any other time; although, with- 

 out 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 afterward reab- 

 sorbed) or permanently. 



Respecting 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- 

 aifected, chyle was no longer well formed; the contents of the lacteals 

 consisting of clear, colorless fluid, instead of being opaque and white, as 

 they ordinarily are, after feeding. 



(b.) It is probable, also, that the moistening of the mucous membrane 

 of the intestines by bile facilitates absorption of fatty matters through it. 



(c.) The bile, like the gastric fluid, has a considerable antiseptic 

 power, and may serve to prevent the decomposition of food during the 

 time of its sojourn in the intestines. Experiments show that the con- 

 tents of the intestines are much more foetid after the common bile-duct 

 has been tied than at other times; moreover, it is found that the mixture 

 of bile with a fermenting fluid stops or spoils the process of fermentation. 



(d.) The bile has also been considered to act as a natural purgative, 

 by promoting an increased secretion of the intestinal glands, and by 

 stimulating the intestines to the propulsion of their contents. This view 

 receives support from the constipation which ordinarily exists in jaundice, 

 from the diarrhoea which accompanies excessive secretion of bile, and from 

 the purgative properties of ox-gall. 



