538 SPECIAL PHYSIOLOGY. 



of the gland ; whilst its narrow end or neck, directed, beneath that 

 organ, upwards, backwards, and to the left, is continuous with the 

 cystic duct. Its upper surface is attached to the liver by areolar tis- 

 sue and bloodvessels; the rest is covered by the peritoneum, which 

 therefore furnishes it with a partial serous coat. Its proper walls are 

 composed of interlacing bands of white, fibrous^ and areolar tissue, 

 intermixed with elastic fibres, and longitudinal and circular unstriped 

 muscular fibres. Within this areolar coat is tl^B mucous coat, which 

 has a peculiar pitted or alveolar aspect, owing to the presence of in- 

 numerable fine ridges, which bound polygonal depressions of various 

 size and form ; at the bottom of the largest depressions there are 

 seen, by aid of a lens, the orifices of fine recesses resembling mucous 

 follicles. The mucous membrane of the gall-bladder is usually of a 

 deep yellow color, and is lined by a columnar epithelium. 



The gall-bladder forms a sort of receptacle, or reservoir for such 

 bile as is not immediately required for the purposes of digestion. It 

 has been shown, in animals, in which artificial openings, or fistulse, 

 have been made into the hepatic duct, that bile is being constantly 

 secreted by the liver. In the intervals between the process of diges- 

 tion, the secretion is slow ; but, during digestion, the bile is secreted 

 very rapidly, and at once passes along the hepatic duct, and common 

 bile duct, into the duodenum ; such bile is named hepatic bile. The 

 period of most rapid secretion, in animals, has been variously stated 

 to be from one or two hours, to ten or twelve hours after eating. Ac- 

 cording to observations made by Dalton on a dog, the quantity in- 

 creases suddenly after eating, reaches its maximum in an hour, and 

 then gradually declines; a far larger quantity enters the intestine 

 during the first hour, than in any other equal period. Abstinence 

 lessens the quantity very much. In the intervals between digestion, 

 however, the bile being secreted more scantily, has not sufficient force 

 to pass through the narrow orifice of the common duct, and thus more 

 or less of the secretion enters the gall-bladder ; there, it undergoes 

 inspissation, losing water, and receiving much mucus from the gall- 

 bladder, some having been already added to it, in the ducts. It thus 

 becomes darker, and more viscid, and, in this condition, it is called 

 cystic bile. The mechanical effect of the spiral folds in the cystic 

 duct, on the passage of the bile into, or out of, the gall-bladder, is 

 probably to favor its entrance, and somewhat check its escape. Dur- 

 ing digestion, both cystic and hepatic bile are believed to be employed, 

 and it is supposed that, at that period, the former is pressed out of 

 the gall-bladder, partly by the distended stomach, and partly by the 

 contraction of its own muscular fibres, stimulated in a reflex manner, 

 by the acid chyme passing over the orifice of the common bile duct, 

 the sphincter-like margin of which may be at the same time relaxed. 



The analyses of bile present some discrepancies, which may depend 

 on the difference between the hepatic and the cystic bile. Speaking 

 generally, the bile is a yellowish, or yellowish-green, viscid fluid, having 

 a peculiar smell and a bitter taste. In carnivorous animals, its color is 

 brownish-yellow ; in herbivorous animals, it is generally greenish. The 

 quantity of bile secreted by a man in twenty-four hours is uncertain. 



