FOOD AND DIGESTION. 385 



self, even after division of the vagus. By special methods of investiga- 

 tion Pawlow has found that the inuervation of the pancreas is somewhat 

 similar to that of the salivary glands. Stimulation of both the vagus 

 and sympathetic nerves, under proper conditions, -will cause a flow of 

 secretion, but the secretion is more abundant in the case of the vagus. 

 Both nerves appear to contain secretory fibres; they are more numerous, 

 however, in the vagus, while trophic fibres or those which cause a build- 

 ing up of the secretion materials in the gland cells are more abundant 

 in the sympathetic. In function the nerves are analogous to the chorda 

 tympani and sympathetic of the submaxillary gland. The gland will 

 continue to secrete after the section of all of its nerves, and in this re- 

 spect is said to differ from the salivary glands. The secretion ap- 

 pears to be called forth on the introduction of food into the stomach, 

 when the blood-vessels of the gland become much dilated, and the se- 

 cretion continues, as we have seen, for many hours after a meal; indeed, 

 may be continuous. The pressure of the secretion is not so great as in 

 the case of the salivary glands; the maximum pressure in the duct is 

 said not to exceed 17 mm. of mercury. 



The amount of secretion per diern is not definitely known but is ap- 

 proximately estimated to be about half a litre. 



THE LIVER. 



The Liver, the largest gland in the body, situated in the abdomen 

 on the right side chiefly, is an extremely vascular organ, and receives 

 its supply of blood from two distinct sources, viz., from the portal vein 

 and from the hepatic artery, while the blood is returned from it into the 

 vena cava inferior by the hepatic veins. Its secretion, the Mle, is con- 

 veyed from it by the hepatic duct, either directly into the intestine, or, 

 when digestion is not going on, into the cystic duct, and thence into 

 the gall-bladder, where it accumulates until required. The portal vein, 

 hepatic artery, and hepatic duct branch together throughout the liver, 

 while the hepatic veins and their tributaries run by themselves. 



On the outside, the liver has an incomplete covering of peritoneum, 

 and beneath this is a very fine coat of areolar tissue, continuous over 

 the whole surface of the organ. It is thickest where the peritoneum is 

 absent, and is continuous on the general surface of the liver with the 

 fine and, in the human subject, almost imperceptible areolar tissue in- 

 vesting the lobules. At the transverse fissure it is merged in the areolar 

 investment called Glisson's capsule, which, surrounding the portal vein, 

 hepatic artery, and hepatic duct, as they enter at this part, accompanies 

 them in their branches through the substance of the liver. 



Structure. The liver is made up of small roundish or oval portions 

 25 



