BILE, an animal fluid of a greenish colour, viscid consistence, and bitter taste.
The organ by which the bile is secreted is the liver. The liver is distinguished by two peculiarities : first, it is the largest gland in the body; and secondly, it is provided with two distinct sets of veins. The veins .that receive the blood front the viscera of the abdomen, that is, from the organs more immediately concerned in the process of digestion, unite together into a large trunk named the vont port-as This vein penetrates into the substance of the liver, and ramifies through it in the manner of an artery ; at the same time the liver receives a large quantity of arterial blood by the hepatic artery. [LIVER.] The ultimate branches of the vena port terminate partly in n sot of vessels termed the hepatio ducts, which contain the bile, and partly in a set of venaela termed the hepatic veins, by which a largo portion of the blood of the vena porta; is transmitted by the ordinary course of the circulation into the vena cave, the great vein that returns the blood from all parts of the body to the right side of the heart. [CIRCULATION OF TUE BLOOD.] Thin arrangement is peculiar. There is no other gland in tho body in which the disposition of the blood-vessels is at all analogous : there is no other instance in which a vein is sent to a gland and distributed to it in the manner of an artery. This peculiarity has naturally led physiologists to infer that the vein in this case performs the ordinary functions of an artery ; that it carries on the process -of aecretiou, and eliminates its product, the bile, out of venous blood.
But whatever doubts physiologists may entertain by which of the two great vessels of the liver the bile is secreted, the consent is universal that the liver is the gland by which this fluid is formed. When duly elaborated in this organ, the bile is received from the secreting vessels by exceedingly minute tubes, the union of which constitutes the excretory duct of the gland, which is termed tho hepatic duct. The hepatic duct passing on towards the duodenum, which, physiologically considered, is a second stomach [ DeonEsrst), communicates with a small membranous cyst or bag, called the gall bladder, a reservoir for the bile. The duct of the gall-bladder, called
the cystic duct, unites with the hepatic duct, and both together form a single tube, termed the choledoch duet, which pierces the duodenum. Thus the hepatic duct, carrying the bile away (rein the liver, either conveys it into the gall-bladder by means of the cystic duct, or transmits it immediately into the duodenum by means of the chole doch duct. The bile which flows immediately into the duodenum is called the hepatic bile; that which is contained in the gall-bladder is called the cystic bile. There is a striking difference in the externul characters of the two, cystic bile being of a much deeper colour, and much more viscid, pungent, and bitter than hepatic bile ; but the difference in their chemical properties, if there he any, has not been ascertained : hepatic bile, on account of the difficulty of collecting it in sufficient quantity, has not been analysed, while some portion of bile is generally found in the gall-bladder after death.
From actual experiment it would appear that the secretion of bile is continually going on in the living system. In whatever circum stances an animal is placed—if the orifice of the choledoch duct be laid bare—the bile is always seen to be flowing drop by drop into the intestine. It is observed to flow much faster during the process of digestion than when the stomach is empty; rind there is reason to believe that, during the digestive process, the hepatic bile is secreted in much larger quantity than when the stomach ie empty, and that it is then conveyed directly into the duodenum. The gall-bladder fills when the stomach is empty, and when the stomach is full the gall-bladder becomes comparatively empty. The gall-bladder, however, is seldom if ever completely emptied. Vomiting contributes more perhaps than any other action of the system to the expulsion of its contents. Magendie states that he has often found it completely empty in animals that died from the effects of an emetic poison.