MECHANISM OF THE SECRETION OF BILE. 439 



Nerves and Lymphatics of the Liver. The nerves of the liver are derived from the 

 pneumogastric, the phrenic, and the solar plexus of the sympathetic. The branches of 

 the left pneumogastric penetrate with the portal vein, while the branches from the right 

 pneumogastric, the phrenic, and the sympathetic surround the hepatic artery and the 

 hepatic duct. All of these nerves penetrate at the transverse fissure and follow the 

 blood-vessels in their distribution. They have not been traced farther than the terminal 

 ramifications of the capsule of Glisson, and their exact mode of termination is unknown. 



The lymphatics of the liver are very numerous. They are divided into two layers: 

 the superficial layer, situated just beneath the serous membrane ; and the deep layer, 

 formed of a plexus surrounding the lobules and situated outside of the blood-vessels. 

 The superficial lymphatics from the under surface of the liver, and that portion of the deep 

 lymphatics which follows the hepatic veins out of the liver, pass through the diaphragm 

 and are connected with the thoracic glands. Some of the lymphatics from the superior 

 or convex surface join the deep vessels that emerge at the transverse fissure and pass 

 into glands below the diaphragm, while others pass into the thoracic cavity. 



Mechanism of the Secretion and Discharge of Bile. The liver has no analogue in the 

 glandular system, either in its anatomy or in its physiology. There is no gland in the 

 economy which we know to have two distinct functions, such as the secretion of bile and 

 the production of certain elements destined to be taken up by the current of blood as it 

 passes through. In other words, there is no organ in the body which has at the same 

 time the functions of an ordinary secreting gland and a ductless gland. If we regard the 

 liver-cells as the anatomical elements which produce the bile, it is evident that their 

 number is very much out of proportion to the amount of bile secreted ; and the liver 

 itself is an organ of much greater size than it seems to us would be required for the mere 

 secretion of bile. We explain this disproportionate size by the fact that the liver has 

 other functions, which are those of a ductless gland. 



There is no gland in which the arrangement of secreting tubes is the same as in the 

 liver. It is hardly possible that the intercellular plexus of fine tubes in the lobules should 

 be any thing but the plexus of origin, or the secreting portion of the hepatic duct. These 

 are certainly not blood-vessels, and the only vessels that could have the appearance we 

 have described, except the bile-ducts, are the lymphatics ; but the communication be- 

 tween these vessels and the excretory bile-ducts, and the fact that they have been seen 

 distended with bile in icteric livers, are pretty conclusive evidence of their nature. This 

 arrangement, then, must be regarded as peculiar to the liver, as the arrangement of a 

 capillary plexus surrounded with cells and enveloped in a dilated extremity of a secreting 

 tube is peculiar to the kidney and is found in no other glandular organ. 



Do the liver-cells, situated outside of the plexus of origin of the biliary duct, secrete 

 the bile, which is taken up by these delicate vessels and carried to the excretory biliary 

 passages? There are very good reasons for answering this question in the affirmative ; 

 although, if we do, we must recognize the fact that the same cells produce glycogenic 

 matter. As far as we are able to understand the mechanism of secretion (except in the 

 production of milk), it seems necessary that a formed anatomical element, known as a 

 secreting cell, should elaborate, from materials furnished by the blood, the elements of 

 secretion ; and this cannot be accomplished by a structureless membrane like that which 

 forms the walls of the bile-ducts. Under this view, assuming that bile, as bile, first 

 makes its appearance in these little lobular tubes, the liver-cells are the only anatomical 

 elements capable of producing the secretion. With regard to the mechanism of this 

 secreting action, we have nothing to say beyond our general remarks in a previous 

 chapter. With the view we have just expressed, certain elements of the bile are sep- 

 arated from the blood, and others are manufactured out of materials furnished by the 

 blood by the liver-cells and are taken up by the delicate plexus of vessels situated between 

 the cells. The discharge of the fluid is like the discharge of any other of the secretions, 



