DIGESTION. 371 



all, and whether it should not be regarded merely as an excre- 

 tion, poured into the alimentary canal to be got rid of. But 

 there are many reasons against such a view. In the first place, 

 the entry of the bile into the upper end of the small intestine 

 where it has to traverse a course of more than twenty feet 

 before getting out of the Body, instead of its being sent into 

 the rectum, close to the final opening of the alimentary canal, 

 makes it probable that it has some function to fulfil in the 

 intestine. Moreover, a great part of the bile, including prac- 

 tically all the bile salts, poured into the intestines is again 

 absorbed from them ; this seems to show that part of the bile 

 is secreted for some other purpose than mere elimination 

 from the Body. One subsidiary use is to assist, by its alka- 

 linity, in overcoming the acidity of the chyme, and so to 

 allow the trypsin of the pancreatic secretion to act upon pro- 

 teids. Constipation is, also, apt to occur in cases where the 

 bile-duct is temporarily stopped, so that bile probably helps to 

 excite the contractions of the muscular coats of the intestine;* 

 under similar circumstances putrefactive decompositions are 

 apt to occur in the intestinal contents. Apart from such sec- 

 ondary influences,however, the bile probably has some influence 

 in promoting the absorption of fats. If one end of a capillary 

 glass tube, moistened with water, be dipped in oil, the latter will 

 not ascend in it, or but a short way; but if the tube be moist- 

 ened with bile, instead of water, the oil will ascend higher in 

 it. So, too, oil passes through a plug of porous clay kept moist 

 with bile, under a much lower pressure than through one wet 

 with water. Hence bile, by soaking the epithelial cells lining 

 the intestine, may facilitate the passage into the villi of oily 

 substances. At any rate, experiment shows that if the bile 

 be prevented from entering the intestine of a dog, the animal 

 eats an enormous amount of food compared with that 

 amount which it needed previously; and that of this food a 

 great proportion of the fatty parts passes out of the alimen- 

 tary canal unabsorbed. There is no doubt, therefore, that 

 the bile somehow aids in the absorption of fats, but exactly 

 how is uncertain. Its possible action in exciting the muscles 

 of the villi to contract will be referred to presently. 



The Intestinal Secretions or Succus Entericus. These 

 consist of the secretions of the glands of Brunner and the 

 crypts of Lieberkiihn. It is difficult to obtain them pure; in- 

 deed the product of Brunner's glands has never been obtained 



