532 DIGESTION 



musculature and the relaxation of the muscular fibers surrounding the 

 duct in the duodenum. If this reciprocal innervation fails to operate 

 properly, discharge of bile into the duodenum may become obstructed 

 so that a certain amount passes back into the blood, as in cases of bile- 

 duct obstruction. 



Bile also contains a certain amount of l&oithiii and other phospholipins. 

 The amount varies considerably in the bile of different animals, even in 

 animals of the same species. It is probably derived, as already men- 

 tioned, like the cholesterol, from the breaking-down of red blood cor- 

 puscles that goes on in the liver. It is no doubt digested by the ferments 

 of the intestinal tract, the liberated cholin, since it is toxic if absorbed, 

 being further attacked by bacteria so as to become converted into cer- 

 tain substances of a nontoxic nature. 



