THE DIGESTIVE JUICES 89 



THE BILE 



Bile is the secretion of the liver which is poured into the duo- 

 denum : it has been collected in living animals by means of a 

 biliary fistula ; the same operation has occasionally been performed 

 in human beings. At death the gall bladder yields a good supply 

 of bile which is more concentrated than that obtained from a 

 fistula. 



Bile is being continuously poured into the intestine, but there 

 is an increased discharge immediately on the arrival of food in 

 the duodenum ; there is a second increase in secretion a few hours 

 later. 



Though the chief blood supply of the liver is by a vein (the portal 

 vein), the amount of blood in the liver varies with its needs, being 

 increased during the periods of digestion. This is due to the fact 

 that in the area from which the portal 



vein collects blood stomach, intestine, / v ^g ^ . 



spleen, and pancreas the arterioles are 

 all dilated, and the capillaries are thus / m 



B * "* 



gorged with blood. Further, the active , 1 

 peristalsis of the intestine and the " A 

 pumping action of the spleen are ad- 

 ditional factors in driving more blood 

 onwards to the liver. 



The bile is secreted from the portal 



FIG. 24. Hcematoidin crystals. 



blood at a much lower pressure than 



one finds in glands, such as the salivary glands, the blood supply 

 of which is arterial. Heidenhain found that the pressure in the bile 

 duct of a dog averaged 15 mm. of mercury, which is about double 

 that in the portal vein. 



The second increase in the flow of bile that which occurs some 

 hours after the arrival of the semi-digested food (chyme) in the 

 intestine was at one time attributed to the effect of the digestive 

 products carried by the blood to the liver stimulating the hepatic 

 cells to activity: this was supported by the fact that protein food 

 increases the quantity of bile secreted, whereas fatty food, which 

 is absorbed, not by the portal vein, but by the lacteals, has no 

 such effect. The facts are now more readily explained by the 

 circumstance that secretin is a stimulant of the liver as well as of 

 the pancreas. 



The chemical processes by which the constituents of the bile are 

 formed are obscure. We, however, know that the biliary pigment is 



