492 DIGESTION 



continued taking milk, the lactase disappears from the pancreatic juice. 

 Attempts have been made to bring it back by feeding the adult upon 

 milk, but without success. Occasionally the pancreatic juice also con- 

 tains invertase. 



The Bile 



Associated with the pancreatic juice in all its functions is the bile. 

 When this fluid is prevented from entering the intestine, the digestive 

 process becomes very imperfect, the absorption of fat being particularly 

 interfered with (see page 691). Bile is also an excretory product, and 

 its composition therefore is much more complex than that of the other 

 digestive fluids. This varies very much, however, according to the 

 method of collection. Bile from the gall bladder after death contains 

 much more solid material, particularly bile salts and mucin, than that 

 collected from a fistula of the bile duct or gall bladder during life. 

 These differences will be evident from the accompanying table. 



Bile from 



Gall bladder Fistula 



100 parts contain 



Water 86 97 



Solids 14 3 



Organic salts (bile salts) 9 0.9-1-8 



Mucin and bile pigment 3 0.5 



Cholesterol ' 0.2 0.06-0.16 



Lecithin and fat 0.5-1.0 0.02-0.09 



Inorganic salts 0.8 0.7-0.8 



In general it may be said that bile obtained from a fistula in man 

 contains only about 3 per cent of total solids, of which from one-fourth 

 to one-half are inorganic, whereas bile from the gall bladder contains 

 10 to 20 per cent of total solids, of which only about one-twentieth are 

 inorganic. The chief cause for this difference appears to be that when 

 the bile goes to the intestine, a considerable proportion of its bile salts 

 is reabsorbed into the portal blood and reexcreted by the liver. Some 

 of the difference may also be caused by the fact that absorption of 

 water takes place from the gall bladder, and that mucin and possibly 

 cholesterol are secreted by this organ. These striking differences be- 

 tween fistula and gall-bladder bile are observed only when the com- 

 mon bile duct is occluded. If the bladder fistula is made with the com- 

 mon duct left open, some of the bile gains entry to the duodenum and 

 therefore becomes reexcreted. It is well known that a fistula of the gall 

 bladder in man after a time closes up and the bile again takes its usual 

 course along the bile duct into the duodenum. 



