CHAPTER IX. 



BILE. 



THE bile is secreted continuously by the liver and passes into the 

 intestine through the common bile duct which opens near the 

 pylorus. Bile is not secreted continuously into the intestine. In a 

 fasting animal no bile enters the intestine, but when food is taken 

 the bile begins to flow; the length of time elapsing between the 

 ingestion of the food and the secretion of the bile as well as the 

 qualitative and quantitative characteristics of the secretion de- 

 pending upon the nature of the food ingested. Fats, the extrac- 

 tives of meat and the protein end-products of gastric digestion, 

 (proteoses and peptones) cause a copious secretion of bile, whereas 

 such substances as water, acids and boiled starch paste fail to do 

 so. In general a rich protein diet is supposed to increase the 

 amount of bile secreted, whereas a carbohydrate diet would cause 

 a much less decided increase and might even tend to decrease the 

 amount. It has been demonstrated by Bayliss and Starling that 

 the secretion of bile is under the control of the same mechanism 

 that regulates the flow of pancreatic juice (see p. 140). In other 

 words, the hydrochloric acid of the chyme, as it enters the duodenum 

 transforms prosecretin into s.ecretin and this in turn enters the 

 circulation, is carried to the liver and stimulates the bile-forming 

 mechanism to increased activity. 



We may look upon the bile as an excretion as well as a secretion. 

 In the fulfillment of its excretory function it passes such bodies 

 as lecithin, metallic substances, cholesterol and the decomposition 

 products of haemoglobin into the intestine and in this way aids in re- 

 moving them from the organism. The bile assists materially in 

 the absorption of fats from the intestine by its solvent action on 

 the fatty acids formed by the action of the pancreatic juice. 



The bile is a ropy, viscid substance which is alkaline in reaction 

 to litmus, 1 and ordinarily possesses a decidedly bitter taste. It 

 varies in color in the different animals, the principal variations being 

 yellow, brown and green. Fresh human bile from the living 

 organism ordinarily has a green or golden-yellow color. Post- 



1 It does not contain any free hydroxyl ions, however. 



150 







