With regard to the evidence of experimental operations upon living animals, this must at all times be unsatisfactory and inconclusive from the difficulty of observing and apprecia ting the consequences of the experiment, and from the morbid condition impressed upon the animal by the serious nature of the operations themselves Those which have been performed are favourable to the conclusion that the bile is separated from the blood of the portal vein. But I have little faith in such experiments ;— after the ligature of the portal vein, the animal lives but a short period ; the blood arrested in its current is conveyed through the medium of inosculations into the general venous circula tion, and then, as I have above suggested, if the animal survive sufficiently long, the bile may be secreted from the fluid which contains it, viz. from the arterial blood.
Cnvier entertains the opinion, that the bile is secreted from venous blood, as may be per ceived in the following passages: "Le foie des animaux vertebras a en effet un caracthre qu'il ne 'mirage avec aucune autre glande ; c'est que sa secretion est alirnentee par du sang veineux; par du sang qui a deja circule, et qui nest pas retournd au cceur, ni par consequent au poumon. Cette circonstance a lieu, non-seulement dans des animaux a circulation double, o4 tout he sang dolt repasser par le poumon, avant de se rendre aux parties, le foie excepte; mais encore dans les animaux A. circulation simple (les reptiles), oa une si grande portion du sang arteriel n'a point retourne au poumon, et tient par consequent de la nature veineuse ; c'est presque alors du sang deux fois veineux qui se rend dans le foie." May we not, therefore, from the powerful arguments afforded by anato mical investigation, and from our knowledge of the compensating energies. aroused by nature in cases of anomaly,—may we not, at least until weightier reasons to the contrary shall be developed by the progressive discoveries of our improving science, conclude that the bile is secretedjivm venous blood I The quantity of the bile is a question diffi cult to decide accurately ; it would appear to be secreted most abundantly during digestion, when the augmented activity of the stomach would seem to be communicated to its neigh bouring organ, the liver. Certainly it is eva cuated from the gall-bladder into the digestive canal at that period. In animals which have been kept long fasting the gall-bladder is always greatly distended. Schultz observed, in an ox which had been kept for some time without food, from twelve to sixteen ounces of bile in the gall-bladder, and in another, after digestion, from two to four ounces only. In a dog which had not eaten for some time he found five drachms, in another, after digestion, about two drachms. In a case of abscess of the liver communicating with the gall-bladder and lung, recorded by Dr. Mom, the whole of the bile flowed through the fistulous canal and was discharged by coughing, " in proof of which," he says, " the faces were of the same whitish colour and had as little smell as those of a person deeply jaundiced. The quantity of bile discharged by coughing was different at different times. It was always greater after meals, and especially for an hour or two after dinner. The quantity expectorated could not be measured with great accuracy from being mixed with mucus and saliva. The whole quantity in twenty-four hours was from ten to fifteen ounces ; and, in this case, I had an opportunity of observing the effects of certain articles of food, and in particular of acids, of wine, and of different fruits, in increasing the quantity of bile." Expulsion of the bile.—This process I have just shewn takes place more abundantly during digestion than at any other period. In all carnivorous and in most herbivorous animals there exists a peculiar provision for the col lection of the bile during the period of ab stinence, in a membranous reservoir, the gall bladder. Some herbivorous animals, deprived of a distinct gall-bladder, have a compensating dilatation upon the hepatic duct. The use of this organ is to retain the bile until digestion demands its excretion. Those animals, there fore, that are provided with it are such as perform the function of digestion at variable intervals. But in those whose digestion is con tinuous, as is the case in many herbivore, the bile flows as it is secreted into the alimentary canal ; being very probably provided more abundantly under the stimulus of a full sto mach than during the abstinence from food or during sleep. In the contracted state of the
duodenum the small and oblique opening of the ductus communis choledochus is closed to the passage of the fluid; it therefore regurgitates along the cystic duct into the gall-bladder. In the slight ascent along this tube it is facilitated by the spiral valve, which also serves to restrain its too sudden emission during spasmodic ac tion of the abdominal muscles. As soon as the duodenum becomes filled with the chyme from the stomach, the opening of the ductus communis choledochus is less compressed. The distension of the stomach, but more particu larly the passage of the chyme along the py lorus into the upper part of the duodenum, causes a gentle pressure upon the coats of the gall-bladder which favours its emission ; its contents are gradually expressed, and flowing along the ductus communis choledochus are mingled with the pulpy mass in the duodenum. This explanation of the process seems to have been entertained by Haller, and to have arisen in his mind from the consideration of the ana tomy of the serpent, where the gall-bladder is far removed from the liver and is situated in the space formed by the contraction of the py lorus and its termination in the small intes tine. Neither do I consider its truth invali dated by those cases in which the g-all-hladder is partly imbedded in the liver, for in such instances that portion of the liver is compressed which immediately covers the fundus of the gall-bladder, or a part of the gall-bladder is exposed against which the duodenum may exert an equal compression. Miller conceives that the efferent ducts of glands are surrounded by " an extremely thin layer of muscular sub stance," which, although not demonstrable ana tomically, he thinks to be placed beyond dispute by physiological observations. "The contractile power of the ductus choledochus in birds was known to Rudolphi. By irritating mechanically or by galvanism the ductus choledochus of a bird just dead, I have frequently produced a very strong contraction of it, which continued some minutes, after which the duct resumed its previous state. I have often excited strong local contractions of the ureters likewise, both in birds and rabbits, by the application of a powerful galvanic stimulus. Tiedemann also has seen motions of the vas deferens of a horse ensue on the application of a stimulus. It appears indeed that periodic vermicular motions are performed by the efferent ducts, at least by the ductus choledochus, in birds ; for I have once observed in a bird just killed, contractions of the duct occurring regularly in pauses of several minutes, the tube dilating again in the intervals ; and what was remarkable, the con tractions took place in an ascending direction, namely, from the intestine towards the liver : and this seems to throw some light on the mode in which the bile at certain times, in stead of being expelled into the intestines, is retained and driven into the diverticulum of the duct, namely, the gall-bladder the com plete closure of the mouth of the duct contri butes perhaps to this effect. The discharge of the bile from the gall-bladder during digestion results probably from the mere of the surrounding parts, and the action of the ab dominal muscles, while the mouth of the duct is open : for I doubt if the gall-bladder is con tractile ; I could produce no contraction of it in mammalia and birds even with the most powerful stimulus of a galvanic battery." Dr. Alamo considers the middle coat of the gall bladder in man to contain muscular fibres; the muscular coat in the gall-ducts of the dog and horse are, he observes, quite distinct, and upon irritation he has seen the gall-bladder contract in a living animal so as to resemble an hour glass. Andral thinks that he has perceived muscular fibres in the hypertrophied coats of the gall-bladder, and Ferrus records a case as occurring to Amussat where, in obstruction to the ductus choledochus by a gall-stone, the middle coat of the gall-bladder and ducts above the impediment was evidently muscular. This preparation was seen by Kiernan at the time that it occurred. The bile during its stay in the gall-bladder becomes inspissated by the removal of the fluid part of the secretion, which is most probably taken up by the numerous lymphatics which cover its surface.