238 PHYSIOLOGY OF ALIMENTATION. 



but not at an even rate, fluctuating in quantity with varia- 

 tions in the nature of the food. 



When different food substances are fed separately to a dog 

 operated upon as indicated above, it is found that neither 

 water, acids, raw white of egg, nor boiled starch as a thick or 

 a thin paste causes a flow of bile. Fat, however, and to a 

 less extent extractives of meat, and the digestion products 

 of white of egg set up a free discharge of the secretion. The 

 bile, therefore, is not unlike the gastric or pancreatic juice, 

 which has each its specific excitants. 



How now do the various substances which bring about a 

 secretion of bile into the intestine do this? The explana- 

 tion which has been and is given ordinarily is that the bile 

 flows in consequence of a nervous reflex which is initiated 

 through the action of certain constituents of the intestinal 

 contents upon the mucous membrane of the duodenum. It 

 is much more probable, however, that the connection between 

 duodenum and liver is of a chemical character. This is shown 

 by the experiments of BAYLISS and STARLING, who find that 

 pancreatic secretin not only augments the flow of pancreatic 

 juice but also the discharge of bile into the intestine. It is 

 an interesting fact that the pancreas and liver should have 

 such a common excitant, for as will be shown immediately 

 the bile augments in a most marked way the digestive prop- 

 erties of the pancreatic juice. 



2. The physiological importance of the bile is shown very 

 clearly in the classical observation of CLAUDE BERNARD and 

 the more modern one of DASTRE. 1 CLAUDE BERNARD noticed 

 that in rabbits, in which the opening of the pancreatic duct 

 into the intestine lies some 30 cm. below that of the bile- 

 duct, the absorption of fat after a fatty meal does not begin 

 until the food has passed the pancreatic duct, for while the 

 lymph leaving the intestine below this point is milky in ap- 

 pearance that above it is clear. This shows that the bile 



1 DASTRE: Arch, de phys. norm, et path., 1890, XXII, p. 315. 



