344 THE HUMAN BODY. 



bile probably has some influence in promoting the absorp- 

 tion 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 moistened 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 sub- 

 stances. 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 ali- 

 mentary 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 pres- 

 ently. Bile precipitates from solution, not only pepsin, but 

 any peptones contained in the chyme which enters the in- 

 testine from the stomach. 



The Intestinal Secretions or Succus Entericus. This 

 consists of the secretions of the glands of Brunner and the> 

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

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

 tained unmixed. That of the crypts of Lieberkiihn is 

 watery and alkaline, and poured out more abundantly duis 

 ing digestion than at other times. It has no special action 

 on starches, most proteids, or on fats; but is said to dissolve 

 blood fibrin and convert it into peptone, and to change cane 

 into grape sugar, a transformation the object of which is 

 not very clear, since cane sugar is itself readily soluble and 

 diffusible. 



Intestinal Digestion. Having considered separately the 

 actions of the secretions which the food meets with in the 

 small intestine we may now consider their combined effect. 



The neutralization of the chyme, followed by its conver- 

 sion into alkaline chyle, will prevent any further action of 

 the pepsin on proteids, but will allow the ptyalin of the 



