274 DIGESTION 



edly by bleeding, the quantity of bile secreted is diminished; at the same 

 time, however, the percentage of solids increases. Cutting down the supply 

 of blood by tying off several branches of the portal vein likewise diminishes 

 the secretion. And when the vena cava inferior is compressed so that the 

 volume of blood passing through the liver in a unit of time is materially 

 reduced the same result is obtained. 



The secretion of the bile declines on stimulation of the spinal cord, because 

 of excitation of the vasoconstrictor nerves to the abdominal viscera, and a con- 

 sequent fall in the blood supply to the liver. Section of the cervical cord pro- 

 duces a general fall of pressure throughout the vascular system and is accom- 

 panied by a decline in the output of bile. The output, on the other hand, 

 increases after section of the splanchnic, because, in spite of the fall in general 

 blood pressure, the blood supply to the liver increases on account of the dilatation 

 of the portal vessels. 



These and other kindred facts can be fully explained by variations of blood 

 supply and contain no proof whatever that the secretion of bile is directly 

 affected by secretory nerves. It is possible also that the rise of the secretion 

 mentioned by some authors as beginning shortly after the ingestion of food, is 

 produced by the dilatation of stomach and intestinal vessels during digestion. 



We may summarize the facts thus far discussed as follows : The liver 

 secretes bile continuously. This secretion is intensified by abundant supply 

 of blood, also by certain bile-producing substances, especially the digestive 

 products of proteids. There is yet at hand no single observation which would 

 permit us to speak of any influence of secretory nerves on the liver. Like 

 the other digestive fluids, bile represents an elaborated product of the secret- 

 ing cells of the gland, for its specific constituents do not occur in the blood. 

 The secretion pressure of the bile also is higher than the blood pressure in the 

 portal vein. 



Since the liver receives blood from several sources (hepatic arteries, portal 

 vein and by return flow from the inferior vena cava), it is of interest to inquire 

 whether any one of these vessels is indispensable to the production of bile, or 

 whether all three can maintain the secretion independently. On closing off the 

 hepatic arteries, secretion still takes place in abundance. Likewise after liga- 

 tion of the portal feeding one of the lobes of the liver, the arterial branch sup- 

 plying the same lobe alone mediates the secretion. Eck has shown that by an 

 operation (Eck fistula) the portal blood can be conducted directly to the inferior 

 vena cava, thus evading the liver altogether; and Stolnikow has found that 

 secretion of bile continues after such an operation. This secretion occurs at 

 least in part at the expense of blood flowing backward in the hepatic veins. Eor 

 if the hepatic artery is tied off after the new route for the blood is established, 

 the secretion still continues. It ceases however when the hepatic vein in addi- 

 tion is tied. Either kind of blood therefore seems to be sufficient to produce bile. 



The hepatic artery supplies the gall bladder, the bile ducts and the inter- 

 lobular branches of the portal vein with blood through its vasa nutritia. When 

 these are ligated and the arterial blood supply thus completely stopped, multiple 

 necrotic foci make their appearance in the liver. From the larger foci cysts 

 develop; the smaller ones become transformed into connective tissue, and are 

 followed finally by an hepatic cirrhosis. 



When the discharge of bile into the intestine is prevented, the bile is reab- 



