THE INTESTINE. 



425 



MEASURES INFLUENCING DIGESTION IN THE DUODENUM. 



CHAPTER VI. 



THE INTESTINE. 



WE now proceed to the consideration of therapeutical 

 methods founded on a more complex physiological basis, 

 namely, the actions and uses of purgatives and intestinal astrin- 

 gents. 



I. PHYSIOLOGICAL RELATIONS. 



As the chyme passes along the small intestine, the chyle 

 and other soluble constituents are absorbed, and what remains 

 is moved onward into the great intestine, where it forms the 

 bulk of the faeces. Along the whole route, fluid is passing in 

 both directions between the intestinal contents and the blood 

 from the bowel into the vessels, and from the vessels into the 

 bowel. The consistency of the faeces will, therefore, depend 

 upon the activity of absorption, the activity of excretion, and, 

 manifestly, the rate pf transit. The more active the absorp- 

 tion, the less active the secretion, and the slower the rate of 

 transit, so much the firmer will be the faeces ; whilst liquidity 

 of the faeces will be the result of imperfect absorption, excessive 

 excretion, or rapid transmission. We are accustomed to speak 

 of the one extreme as constipation, and of the other as diarrhoea. 



Absorption from the bowel is carried on by the lacteal and 

 portal systems. The great bulk of the water and salts 

 enter the portal system, by a process of diffusion or osmosis. 

 The activity of this process varies greatly with the amount of 

 water, salts, and proteids in the bowel, as compared with the 

 blood plasma ; with the chemical nature of these salts ; with 

 the rate of the circulation through the veins that is, with the 

 state of the liver ; and with the condition of the membranes 

 through which the fluids pass. 



Excretion is so active in the small intestine that the faeces 



