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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 

 from 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 vena portse. 

 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. The ultimate branches of the vena 

 portse terminate partly in a set of vessels termed the he- 

 patic ducts, which contain the bile, and partly in a set of 

 vessels termed the hepatic veins, by which a large portion 

 of the blood of the vena ports) is transmitted by the ordi- 

 nary course of the circulation into the vena cava, the great 

 vein that returns the blood from all parts of the body to 

 the right side of the heart. [See CIRCULATION.] 



This arrangement is peculiar. There is no other gland 

 in the 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 func- 

 tion of an artery ; that it carries on the process of secretion, 

 and eliminates its product, the bile, out of venous blood. 

 And this inference is strengthened by the following con- 

 siderations: 



1 . A large portion of the ultimate branches of the vena 

 portse terminate, as has been stated, in the hepatic ducts, 

 that is, the excretory ducts of the gland, or the tubes 

 provided for carrying away the secreted fluid after its ela- 

 boration. 



2. The elements of which the bile is composed abound 

 more in the blood of the vena portso than in that of the 

 hepatic artery. The chief constituent elements of the bile 

 are hydrogen and carbon. These two elements always 

 abound more in venous than in arterial blood, the venous 

 blood acquiring them as it flows slowly along the course of 

 the circulation, and acquiring them the more abundantly 

 the slower the stream and the longer its course. 



3. The distinctive character of every secreting organ is 

 that it receives a copious supply of blood-vessels and nerves. 

 Accordingly the ramifications of the vena portso receive a 

 much greater supply of arterial capillaries from the hepatic 

 artery than is observed with respect to any other vein in 

 the body, and a correspondingly greater supply of ganglial 

 or organic nerves than venous capillaries in general ; these 

 nerves being, as will be shown hereafter, the source whence 

 the blood-vessels derive their vital endowments, and are 

 capable of producing those complicated changes which the 

 blood undergoes during the process of secretion. 



These considerations go far to show that the secretion of 

 the bile is an anomaly in the animal economy, inasmuch 

 as it is elaborated by a vein out of venous blood ; but there 

 are many eminent physiologists to whose minds they do 

 not appear of sufficient weight to warrant this conclusion. 

 Bit-hat, for instance, contends, and adduces plausible argu- 

 ments in favour of the opinion, that the bile is secreted from 

 the hepatic artery ; and Magendie conceives that it is formed 

 at one and the same lime from the blood both of the vena 

 portte and of the hepatic artery. It is certain that cases are 

 on record in which the vena portas is said to have united 

 directly with the vena cava without going to the liver at all ; 

 and that, in such cases, the secretion of bile went on just 

 as well as when the vena portto is distributed in the ordi- 

 nary mode. One such case, clearly made out, would afford 

 a demonstration that bile is capable of being secreted by the 

 hepatic artery. 



But whatever doubt 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 the hepatic duct. The 

 hepatic duct passing on towards the duodenum, which, phy- 

 siologically considered, is a second stomach [see DUODE- 

 NUM], 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 duct, which pierces the duodenum. 



Thus the hepatic duct, carrying the bile away from 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 choledoch duct. The bile which (lows 

 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 external 

 characters of the two, cystic bile being of a much deeper 

 colour, and much more viscid, pungent, and bitter than he- 

 patic bile ; but the difference in their chemical properties, if 

 there be any, has not been ascertained : hepatic bile, on 

 account of the difficulty of collecting it in sufficient quan- 

 tity, has not been analysed, while some portion of bile is 

 generally found in the gall-bladder after death. Some 

 physiologists, indeed, are of opinion that the gall bladder is 

 not passive in the reception of the bile ; that it is not a 

 mere receptacle for this fluid ; that the cystic duct acts as 

 nn absorbent, actually selecting from the bile, as it is flowing 

 in the hepatic duct, its more active ingredients, which are 

 conveyed into the gall bladder, and retained there until 

 needed ; but it is more probable that the blander portions of 

 the bile are absorbed during its retention in the gall bladder, 

 and that while it remains there its elements re-act upon each 

 other so as somewhat to modify the character of the secre- 

 tion, rendering it more viscid, pungent, and bitter than the 

 recently secreted fluid. 



From actual experiment it would appear that the secre- 

 tion of bile is continually going on in the living system. In 

 whatever circumstances 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 ; and there is reason to believe 

 that, during the digestive process, the hepatic bile is se- 

 creted in much larger quantity than when the stomach is 

 empty, and that it is then conveyed directly into the duo- 

 denum. The gall-bladder fills when the stomach is empty, 

 and when the stomach is full the gall bladder becomes com- 

 paratively empty. The gall-bladder, however, is seldom if 

 ever completely emptied. Vomiting contributes more per- 

 haps 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. 



The use which the bile serves in the economy is to pro- 

 duce a specific change upon the aliment, in a pertain stage 

 of the digestive process. The first change which the food 

 undergoes after it has been swallowed is the reduction of it 

 by the stomach into a fluid mass, the appearance of which 

 varies considerably according to the nature of the food. 

 This fluid mass is termed chyme, which when accumulated 

 in a certain quantity is sent from the stomach into the duo- 

 denum. In the duodenum the food undergoes a further 

 change, and is converted from chyme into the substance 

 called chyle. These two fluids are distinguished from each 

 other by specific characters. [See DIGESTION.] The bile 

 is the main agent in producing the change by which chyme 

 is converted into chyle. This is proved by a decisive ex- 

 periment performed by Sir B. Brodie. 



This physiologist applied a ligature around the choledoch 

 duct of an'animal, so as completely to prevent the bile from 

 entering the duodenum, and then noted the effects pro- 

 duced on the digestion of the food immediately before or 

 immediately after the operation. The experiment was re- 

 peated several times, and the result was uniform. The 

 production of the chyme in the stomach took place as usual, 

 but the conversion of the chyme into chyle was immediately 

 and completely interrupted. Not the smallest trace of chyle 

 was perceptible either in the duodenum, or in the vessels 

 which take up the chyle when formed, namely, the lacteals. 

 This experiment is decisive as to the proper office of the 

 bile, which is to separate the nutritious from the non-nutrient 

 or excrementitious part of the chyme, and thus to form 

 chyle. In effecting this separation the bile itself is divided 

 into two parts; its coloured and bitter portion passes on 

 along with the excrementitious part of the chyme into the 

 large intestines, while its albuminous and saline part com- 

 bines with the chyle, is absorbed with it by the lacteals, 

 and is thus carried with it into the circulation. The coloured 

 and bitter portion of the bile which combines with the ex- 

 crementitious part of the chyme, and whicn, together with, 

 certain secretions from the mucous surface of the alimen- 

 tary canal, constitute the faeces, imparts to the fteculent 



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