822 PHYSIOLOGY OF DIGESTION AND SECRETION. 



thoracic duct.* Experimental evidence points to both possibili- 

 ties. The increased pressure in the bile system leads possibly to 

 a rupture of the delicate bile capillaries, and the bile thus escapes 

 into the lymph-spaces. From these spaces it may be absorbed 

 directly by the blood-vessels of the liver, or it may be carried off 

 in the lymph-stream toward the thoracic duct. 



General Physiological Importance of Bile. The physiological 

 value of bile has been referred to in speaking of its several constitu- 

 ents. It is probably of importance both as a medium of excretion 

 and as a digestive secretion. Its value from the former stand- 

 point we know little about. Certain of its constituents, the bile 

 pigments, cholic acid, cholesterin, and lecithin, may appear in the 

 feces more or less modified, but on the other hand these substances 

 may be reabsorbed in part from the intestine, so that it is difficult 

 to say in how far they are to be regarded as excretory products. 

 On the experimental side it can be shown that a number of dyes 

 when introduced into the blood are eliminated or excreted by way of 

 the bile as well as through the urine, a fact which indicates that the 

 liver may act as an excretory organ. As a digestive secretion, the 

 most important function attributed to the bile is the part it takes in 

 the digestion and absorption of fats. It accelerates greatly the action 

 of the lipase of pancreatic juice in splitting the fats to fatty acids and 

 glycerin, and it aids materially in the absorption of the products 

 of this hydrolysis. A number of observers have shown that when a 

 permanent biliary fistula is made, and the bile is thus prevented 

 from reaching the intestinal canal, a large proportion of the fat of 

 the food escapes absorption and is found in the feces. This action of 

 the bile may be referred directly to the fact that the bile acids serve 

 as a solvent for the fats and fatty acids. It was formerly believed 

 that bile is also of great importance in restraining the processes of 

 putrefaction in the intestine. It was asserted that bile is an efficient 

 antiseptic, and that this property comes into use normally in prevent- 

 ing excessive putrefaction. Bacteriological experiments made by a 

 number of observers have shown, however, that bile itself has very 

 feeble antiseptic properties, as is indicated by the fact that it putrefies 

 readily. The free bile acids and cholalic acid do have a direct retard- 

 ing effect upon putrefactions outside the body ; but this action is not 

 very pronounced, and has not been demonstrated satisfactorily for 

 bile itself. It seems to be generally true that in cases of biliary fistula 

 the feces have a very fetid odor when meat and fat are taken in the 

 food. But the increased putrefaction in these cases may possibly be 

 an indirect result of the withdrawal of bile. It has been suggested, 

 for instance, that the deficient absorption of fat that follows upon the 



*See Mendel and Underbill for literature, "American Journal of Phys- 

 iology," 14, 252, 1905. 



