174 MANUAL OF PHYSIOLOGY. 



found greatly distended, because the secretion has continued to 

 flow into that receptacle, and there has been no call for its dis- 

 charge into the duodenum. 



The amount of bile produced by dogs is much influenced by 

 the diet. It is very great when meat alone is consumed, less with 

 vegetable diet, and very small with a diet of pure fat. As a gen- 

 eral rule the bile is more abundantly produced in herbivorous 

 than in carnivorous animals. 



The secretion of bile is also influenced by the amount of blood 

 flowing through the organ. Ligature of the hepatic artery causes 

 cessation of the secretion, and ultimately death, from malnutri- 

 tion of the tissue of the liver. 



These variations in the rate of secretion may depend on direct 

 nervous influence, but no special secretory nerve mechanism has 

 been discovered for the liver, and it is quite possible that the 

 changes in the activity of the gland which accompany the differ- 

 ent periods of digestion may be accounted for by changes in the 

 intestinal blood supply, which give rise to corresponding differ- 

 ences in the amount of blood flowing through the portal vein. 

 If the vena porta be ligatured, an effect corresponding to the 

 magnitude of the vessel is produced, the secretion is arrested, and 

 the animal dies; but it has been said that the secretion continues 

 in the peripheral part of the lobules. If both the portal vein and 

 hepatic artery are ligatured, the secretion at once stops. 



The force with which the bile is secreted is very small. That 

 is to say, the pressure in the ducts never exceeds that of the blood 

 as occurs in the salivary glands ; but, on the contrary, when a 

 pressure of about 16 mm. (.63 in.) mercury is attained, the evac- 

 uation of the bile ceases, and with a little increase of opposing 

 force the fluid in the manometer retreats and finds its way into 

 the blood. The low pressure which can be reached in the gall 

 ducts does not imply any want of secretory power on the part of 

 the liver cells, but merely that there exists a great facility of 

 communication between the duct radicles and the bloodvessels, 

 most probably through the medium of the lymphatics. This is 

 made obvious by experiment, by which it can be shown that with a 

 comparatively low pressure (200 mm. = nearly 8 in. of water for a 



