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separated by filtration from the remaining fluid, is then decomposed in turn by carbonate of soda, and the original glyko-cholate of soda reproduced. The filtered fluid which remains, and which contains the tauro cholate of soda, is then treated with subacetate of lead, which precipitates a tauro-cholate of lead. This is separated by filtration, washed, and decomposed again by carbonate of soda, as in the former case.

The two biliary substances in ox bile may, therefore, be distinguished by their reactions with the salts of lead. Both are precipitable by the subacetate; but the glyko-cholate of soda is precipitable also by the acetate, while the tauro-cholate is not so. If subacetate of lead, therefore, be added to the mixed watery solution of the two substances, and the whole filtered, the subsequent addition of acetate of lead to the filtered fluid will produce no precipitate, because both the biliary matters have been entirely thrown down with the deposit; but if the acetate of lead be first added, it will precipitate the glyko-cholate alone, and the tauro-cholate may afterward be thrown down separately by the subacetate.

These two substances, examined separately, have been found to possess the following properties:

52

Glyko cholate of soda (NaO,CHNO,,) crystallizes, when precipitated by ether from its alcoholic solution, in radiating bundles of fine white silky needles, as above described. It is composed of soda, united with a peculiar acid of organic origin, viz., glyko-cholic acid (C2H42NO,1,HO). This acid is crystallizable and contains nitrogen, as shown by the above formula, which is that given by Lehmann. If boiled for a long time with a dilute solution of potass, glyko-cholic acid is decomposed with the production of two new substances; the first a non-nitrogenous acid body, cholic acid (CHO,,HO); the second a nitrogenous neutral body, glycine (C,H,NO). Hence the name, glyko-cholic acid, given to the original substance, as if it were a combination of cholic acid with glycine. In reality, however, these two substances do not exist originally in the glyko-cholic acid, but are rather new combinations of its elements, produced by long boiling, in contact with potass and water. They are not, therefore, to be regarded as, in any way, natural ingredients of the bile, and do not throw any light on the real constitution of glyko-cholic acid.

Tauro cholate of soda (NaO,C,,H,,NS,O,,) is also a very abundant ingredient of the bile. It is said by Robin and Verdeil' that it is

1 Chimie Anatomique et Physiologique, vol. ii. p. 473.

not crystallizable, owing probably to its not having been separated as yet in a perfectly pure condition. Lehmann states, on the contrary, that it may crystallize,' when kept for a long time in contact with ether. We have not been able to obtain this substance, however, in a crystalline form. Its acid constituent, tauro-cholic acid, is a nitrogenous body, like glyko-cholic acid, but differs from the latter by containing in addition two equivalents of sulphur. By long boiling in a dilute solution of potass, it is decomposed with the production of two other substances; the first of them the same acid body mentioned above as derived from the glyko-cholic, viz., cholic acid; and the second a new nitrogenous neutral body, viz., taurine (C,H,NS,O,). The same remark holds good with regard to these two bodies, that we have already made in respect to the supposed constituents of glyko-cholic acid. Neither cholic acid nor taurine can be properly regarded as really ingredients of taurocholic acid, but only as artificial products resulting from its alteration and decomposition.

The glyko-cholates and tauro-cholates are formed, so far as we know, exclusively in the liver; since they have not been found in the blood, nor in any other part of the body, in healthy animals; nor even, in the experiments of Kunde, Moleschott, and Lehmann on frogs,' after the entire extirpation of the liver, and consequent suppression of the bile. These substances are, therefore, produced in the glandular cells of the liver, by transformation of some other of their ingredients. They are then exuded in a soluble form, as part of the bile, and finally discharged by the excretory hepatic ducts.

The two substances described above as the tauro-cholate and glyko-cholate of soda exist, properly speaking, only in the bile of the ox, where they were first discovered by Strecker. In examining the biliary secretions of different species of animals, Strecker found so great a resemblance between them, that he was disposed to regard their ingredients as essentially the same. Having established the existence in ox bile of two peculiar substances, one crystallizable and non-sulphurous (glyko-cholate), the other uncrystallizable and sulphurous (tauro-cholate), he was led to consider the bile in all species of animals as containing the same substances, and as differing only in the relative quantity in which the two

Physiological Chemistry, Phil. ed., vol. i. p. 209.

? Lehmann's Physiological Chemistry, Phil. ed., vol. i. p. 476.

were present. The only exception to this was supposed to be pig's bile, in which Strecker found a peculiar organic acid, the "hyocholic" or "hyo-cholinic" acid, in combination with soda as a base.

The above conclusion of his, however, was not entirely correct. It is true that the bile of all animals, so far as examined, contains peculiar substances, which resemble each other in being freely soluble in water, soluble in absolute alcohol, and insoluble in ether; and in giving also a peculiar reaction with Pettenkofer's test, to be described presently. But, at the same time, these substances present certain minor differences in different animals, which show them not to be identical.

In dog's bile, for example, there are, as in ox bile, two substances precipitable by ether from their alcoholic solution; one crystallizable, the other not so. But the former of these substances crystallizes much more readily than the glyko-cholate of soda from ox-bile. Dog's bile will not unfrequently begin to crystallize freely in five to six

Fig. 50.

hours after precipitation by ether (Fig. 50); while in ox-bile it is usually twelve, and often twentyfour or even forty-eight hours before crystallization is fully established. But it is more particularly in their reaction with the salts of lead that the difference between these substances becomes manifest. For while the crystallizable substance of ox-bile is precipitated by acetate of lead, that of dog's bile is not affected by it. If dog's bile be evaporated to dryness, extracted with absolute alcohol, the alcoholic solution precipitated by ether, and the ether precipitate then dissolved in water, the addition of acetate of lead to the watery solution produces not the slightest turbidity. If subacetate of lead be then added in excess, a copious precipitate falls, composed of both the crystallizable and uncrystallizable substances. If the lead precipitate be then separated ed with absolute alcohol by filtration, washed, and decomposed, as above described, by carbonate of soda, the watery solution will contain the re-formed soda salts of the bile. The watery solution may then be evaporated to dryness, extracted with absolute alcohol, and the alcoholic solution precipitated by ether; when the ether precipitate crystallizes partially after a time, as in fresh bile. Both the biliary matters of dog's bile

[graphic]

DOG'S BILE, extract

and precipitated with

ether.

are therefore precipitable by subacetate of lead, but neither of them by the acetate. Instead of calling them, consequently, glyko-cholate and tauro-cholate of soda, we shall speak of them simply as the "crystalline" and "resinous" biliary substances.

In cat's bile, the biliary substances act very much as in dog's bile. The ether-precipitate of the alcoholic solution contains here also a crystalline and a resinous substance; both of which are precipitable from their watery solution by subacetate of lead, but neither of them by the acetate.

In pig's bile, on the other hand, there is no crystallizable substance, but the ether-precipitate is altogether resinous in appearance. Notwithstanding this, its watery solution precipitates abundantly by both the acetate and subacetate of lead.

Fig. 51.

In human bile, again, there is no crystallizable substance. We have found that the dried bile, extracted with absolute alcohol, makes a clear, brandy red solution, which precipitates abundantly with ether in excess; but the ether-precipitate, if allowed to stand, shows no sign of crystallization, even at the end of three weeks (Fig. 51). If the resinous precipitate be separated by decantation and dissolved in water, it precipitates, as in the case of pig's bile, by both the acetate and subacetate of lead. This might, perhaps, be attributed to the presence of two different substances, as in ox-bile, one precipitated by the acetate, the other by the subacetate of lead. Such, however, is not the case. For if the watery solution be precipitated by the acetate of lead and then filtered, the filtered fluid gives no precipitate afterward by the subacetate; and if first precipitated by the subacetate, it gives no precipitate after filtration by the acetate. The entire biliary ingredients, therefore, of human bile are precipitated by both or either of the salts of lead.

[graphic]

HUMAN BILE, ex

tracted with absolute ed by ether.

alcohol and precipitat

Different kinds of bile vary also in other respects; as, for example, their specific gravity, the depth and tinge of their color, the quantity of fat which they contain, &c. &c. We have already mentioned the variations in color and specific gravity. The alcoholic solution of dried ox-bile, furthermore, does not precipitate at all on the addition of water; while that of human bile,

of pig's bile, and of dog's bile precipitate abundantly with distilled water, owing to the quantity of fat which they hold in solution. These variations, however, are of secondary importance compared with those which we have already mentioned, and which show that the crystalline and resinous substances in different kinds of bile, though resembling each other in very many respects, are yet in reality far from being identical.

TESTS FOR BILE.

In investigating the physiology of any animal fluid it is, of course, of the first importance to have a convenient and reliable test by which its presence may be detected. For a long time the only test employed in the case of bile, was that which depended on a change of color produced by oxidizing substances. If the bile, for example, or a mixture containing bile, be exposed in an open glass vessel for a few hours, the upper layers of the fluid, which are in contact with the atmosphere, gradually assume a greenish tinge, which becomes deeper with the length of time which elapses, and the quantity of bile existing in the fluid. Nitric acid, added to a mixture of bile and shaken up, produces a dense precipitate which takes a bright grass-green hue. Tincture of iodine produces the same change of color, when added in small quantity; and probably there are various other substances which would have the same effect. It is by this test that the bile has so often been recognized in the urine, serous effusions, the solid tissues, &c., in cases of jaundice. But it is very insufficient for anything like accurate investigation, since the appearances are produced simply by the action of an oxidizing agent on the coloring matter of the bile. A green color produced by nitric acid does not, therefore, indicate the presence of the biliary substances proper, but only of the biliverdine. On the other hand, if the coloring matter be absent, the biliary substances themselves cannot be detected by it. For if the biliary substances of dog's bile be precipitated by ether from an alcoholic solution, dissolved in water and decolorized by animal charcoal, the colorless watery solution will then give no green color on the addition of nitric acid or tincture of iodine, though it may precipitate abundantly by subacetate of lead, and give the other reactions of the crystalline and resinous biliary matters in a perfectly distinct manner.

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