DIGESTION. 191 



THE LIVER. 



The liver is a highly vascular conglomerate gland situated in the right 

 hypochondriac region and connected with the intestine by a duct. 



Inasmuch as the liver performs several functions related to both secretion 

 and excretion, a consideration of its structure and its various functions will 

 be deferred to a subsequent chapter. In this connection only the bile, and its 

 physical properties and chemic composition in relation to the digestive 

 process, will be considered. 



The bile is a product of the secretor activity of the liver cells. As 

 it is poured into the intestine in man and most mammals at a point corre- 

 sponding to the orifice of the pancreatic duct, and most abundantly at the 

 time the food is passing through the duodenum, it is usually regarded as a 

 digestive fluid possessing an influence favorable if not necessary to the com- 

 pletion of the general digestive process. 



Anatomic Relations of the Biliary Passages. After its forma- 

 tion by the liver cells the bile is conveyed from the liver by the bile capillaries, 

 which unite finally to form the main hepatic duct. This duct emerges 

 from the liver at the transverse fissure. At a distance of about 5 centimeters 

 it is joined by the cystic duct, the distal extremity of which expands into a 

 pear-shaped reservoir, the gall-bladder in which the bile is temporarily 

 stored (Fig. 60). The duct formed by the union of the hepatic and cystic 

 ducts, the common bile-duct, passes downward and forward for a distance 

 of about 7 centimeters, pierces the walls of the intestine and passes obliquely 

 through its coats for about a centimeter and opens into a small receptacle, 

 the ampulla of Vater. The ampulla in turn opens on a small papilla into 

 the intestine. The walls of the biliary passages are composed of a mucous 

 membrane internally, a fibrous and muscular coat externally. The termina- 

 tion of the common bile-duct is provided with a distinct band of circularly 

 disposed muscle-fibers, which when in action completely close the orifice 

 and prevent the discharge of bile. It may therefore be regarded as a true 

 sphincter muscle. Small racemose glands are embedded in the mucous 

 membrane of the main ducts. 



Physical Properties and Chemic Composition of Bile. The bile 

 obtained directly from the liver through a cannula inserted into the hepatic 

 duct is always thin and watery, while that obtained from the gall-bladder is 

 more or less viscid from admixture with mucin, the degree of the viscidity 

 depending on the length of time it remains in this reservoir. The specific 

 gravity of human bile varies within normal limits from i.oio to 1.020. 

 The reaction' is invariably alkaline in the human subject when first dis- 

 charged from the liver, but may become neutral in the gall-bladder. The 

 alkalinity depends on the presence of sodium carbonate and sodium phos- 

 phate. When fresh, it is inodorous; but it readily undergoes putrefactive 

 changes, and soon becomes offensive. Its taste is decidedly bitter. When 

 shaken with water, it becomes frothy a condition which lasts for some 

 time and which is due to the presence of mucin. In ox bile the mucin is 

 replaced by a nucleo-proteid. 



The color of bile obtained from the hepatic duct is variable, usually a 

 shade between a greenish-yellow and a brownish-red. In different animals 



