58 DIGESTION. 



lesterin, and is supposed to be a modification of cholesterin by 

 digestion. Whether or not the stercorin (cholesterin) is an excre- 

 tion of the liver corresponding to the urea of the kidney is some- 

 what uncertain. 



What effect has bile upon the digestion? 



(1) The alkaline reaction of the bile aids the pancreatic and checks 

 the pepsin digestion ; it aids in the emulsion of the fats, and is 

 probably very active in this process. (2) It moistens the mucous 

 membrane and favors the absorption of digested food. (3) It acts 

 as a natural purgative and as a natural antiseptic, and in this way 

 is very essential to the proper performance of the digestive process. 

 As a purgative bile acts by stimulating peristalsis. 



What is the effect of the liver upon absorbed chyle ? 



(1) Peptones resulting from the digestion of proteids undergo 

 some modification in the liver, for it is found that if injected into 

 the portal vein they do not appear in the urine, while if injected into 

 the general system they do appear. This matter is not fully under- 

 stood as yet, since the change the peptones undergo in the lym- 

 phatic vessels, to allow absorption without relation to the liver, is 

 still in the dark. 



(2) The liver normally forms a substance resembling starch in its 

 chemical composition. This is known as glycogen, and is formed 

 from glucose taken up by the portal circulation. Its chemical for- 

 mula is that of starch (C 6 H 10 5 ), and it is derived from glucose 

 (C 6 H 12 6 ) by dehydration, and is rapidly changed by diastatic fer- 

 ments to glucose. This process is known as the glycogenic function 

 of the liver : its use is supposed to be the storage of a fund of 

 carbohydrate material (an " animal starch ") to maintain a steady 

 supply to the system. 



What is the duty of the large intestine in digestion ? 



The chyme which enters the large intestine still continues in the 

 influence of the ferments, and the process of digestion continues. 

 The food may undergo acid fermentation here, but there is no new 

 digestive action. That the large intestine may have the power of 

 acting upon food is shown by the absorption of fats, proteids, etc. 

 which are taken in nutrient enemata. 



Describe defecation. 



The expulsion of the refuse of digestion from the intestine is 

 partly a voluntary act, but more especially reflex. The voluntary 



