min in its coagulated state, but it is covered with a pavement of nucleated epithelium cells, which are continually undergoing gradual disintegration and solution. A tough viscid secretion, termed mucus, constantly bathes the surface of these membranes. In this secretion the epithelial particles can be traced in different stages of disintegration. The characters of mucus differ greatly with the surface from which it is obtained; but it usually assumes the appearance of a tough glairy semi-transparent mass, which swells up in water, but is not dissolved by this liquid. To the substance which gives it this glairy consistence the name of mucin has been applied. Mucin is turned yellow by nitric acid; but it differs from albumin, since its solutions are not precipitated by corrosive sublimate: it is also not precipitated from its acid solutions by potassic ferrocyanide until after the acid solution has been boiled. The mucus from the surface of the alimentary canal and its appendages is coagulated by acetic acid and weak acids in general, but it is soluble in alkaline solutions. The mucus from the surface of the urinary organs is dissolved to a certain extent both by acids and by alkalies. Both forms of mucus are immediately coagulated by alcohol, and the secretion presents many characters resembling those of a solution of albumin. Alkaline chlorides are abundant in mucus from the nose; and the phosphates of the alkalies and small quantities of the phosphates of the earths are also present.

(1692) 5. THE BILE.-This important secretion is produced from venous blood by the liver, and in most animals provision is made for its accumulation in a sac connected with the gland, termed the gall-bladder. When taken from this receptacle it constitutes gall, or cystic bile.

It has

Human bile is a ropy liquid of a yellowish-green colour when concentrated, but of a bright yellow when diluted. a peculiar musky odour and a bitter taste. When poured into water it sinks to the bottom, and does not mix readily with it, but it may be mixed with it by agitation, and it then forms a liquid which froths strongly, like a solution of soap. The viscidity of the bile is owing to the presence of a quantity of mucus from the gall-bladder, which it holds in solution. Owing to the presence of this mucus the bile is very prone to putrefaction; but if the mucus be got rid of by coagulation with acetic acid and filtration, or otherwise, the bile may be preserved without decomposition for some time.

Ox bile, owing to the facility with which it may be procured,

THE BILE-GLYCOCHOLIC ACID.

is the variety which has been chiefly examined.

883

It has usually

a sp. gr. of about 1'026, and, according to Berzelius, it contains the following ingredients in 100 parts:

No albumin is present in the bile, but its organic constituents contain a small percentage of nitrogen. It also contains sulphur in notable quantity. It is remarkable that the salts found in the bile of salt-water fishes consist almost exclusively of those of potassium, while the salts of the bile of fresh-water fishes, and of the herbivora, consist chiefly of those of sodium, although, from the circumstances in which the two classes of animals are placed, the opposite results might have been anticipated.

Owing to the facility with which bile undergoes decomposition, the statements of the earlier chemists who examined this liquid were contradictory; but the masterly researches of Strecker have at length removed all doubt respecting the true nature of the biliary secretion. The result of these investigations has been to show that ox bile may be regarded as a species of soap formed by the combination of two peculiar resinoid acids with sodium. Both of these resinous acids (the glycocholic and the taurocholic) contain nitrogen. The taurocholic acid also contains sulphur, but the glycocholic acid is free from this element. Ox bile likewise contains, in addition to the mucus of the gall bladder, minute quantities of cholesterin, and a small amount of stearic, oleic, and lactic acids, united with potassium and ammonium. Besides these substances, a peculiar colouring matter is found in combination with an alkaline base, and a small proportion of a body called lecithin by Strecker, which is characterized by yielding oleophosphoric acid when boiled with baric hydrate (Lieb. Ann., lxv. lxvii. and lxx.).

(1693) Glycocholic Acid [Cholic Acid of Strecker (from xo`ǹ, bile); HEHNO].—This acid constitutes the principal portion of the resinous matter of ox bile; it forms white, voluminous, silky, acicular crystals, which shrink much in drying; it is sparingly soluble in cold water, more freely so in hot water; the solution on cooling deposits crystals, which have a bitterish-sweet taste. Alcohol dissolves it freely, but leaves it as a resinous mass on evaporation: it is very sparingly soluble in ether. The salts

884

THE BILE-GLYCOCHOLIC ACID.

which it forms with the metals of the alkalies and the earths may be crystallized; they are soluble in alcohol.

Glycocholic acid, when boiled with excess of an alkaline liquid, such as solution of baryta, undergoes a remarkable decomposition the whole of the nitrogen is separated in the form of glycocine, which remains in the solution, and a new resinoid acid, the cholic acid of Demarçay (cholalic acid of Strecker), is found in combination with barium :—

Glycocholic acid.

Baric cholate.

Glycocine,

2 HЄHNO + H2O,Ba✪ = Ba 2 H95 + 2 €2H ̧NO.

26 42

6

24 39

The elements of 1 atom of glycocholic acid, with those of I atom of water, contain the elements of 1 atom of cholic acid and I of glycocine; so that the decomposition of glycocholic acid by alkalies is analogous to that of hippuric acid, by acids. If glycocholic acid be boiled with acids it gradually loses water, and becomes converted first into cholonic acid (H4NO,), and then into glycocine and choloidic acid (H79; 1695), and the latter, by a further loss of water, is ultimately converted into dyslysin (E48H7206).

481 78

26 41

Solutions of the normal acetate of lead, of corrosive sublimate, and of nitrate of silver, produce no precipitates in an aqueous solution of glycocholic acid. The salts which it forms with the alkalies are also unaffected by solution of baric chloride; but they are precipitated when mixed with solutions of the salts of copper, of lead, of iron, and of silver. The silver precipitate is somewhat soluble in boiling water, and crystallizes as the solution cools. Acetic and other acids, when added to the solutions of the glycocholates, decompose them, and throw down the acid in the form of a resin. Sodic glycocholate (NaЄHNO) may be obtained in crystals by the addition of three or four times its bulk of ether to its alcoholic solution, but it does not crystallize either from water or from alcohol: it fuses easily to a resinous The crystals have a very characteristic form; they consist of six-sided prisms, with the ends obliquely truncated. The crystallized bile of Platner consists of a mixture of potassic and sodic glycocholates.

mass.

421

Preparation.-Glycocholic acid is not obtained pure without considerable difficulty. Recent ox bile is evaporated, and the residue is dried at a temperature of 248° (120° C.); after which it is digested with cold absolute alcohol. The solution thus obtained is filtered, and ether is added gradually, by which means a brown resinous mass is separated. As soon as the liquid has

THE BILE-CHOLIC ACID.

885 thus deposited most of the colouring matter, it is decanted, and the potassic and sodic glycocholates, which are still retained in solution, are precipitated by the further addition of ether. The liquid becomes milky, a further separation of a resinoid substance occurs, after which the glycocholates are gradually deposited in the form of stellate tufts of needles. These crystals must be washed with anhydrous alcohol, containing one-tenth of its weight of ether, and then dried rapidly in vacuo. In order to obtain the acid, the crystals must be dissolved in water, and precipitated by dilute sulphuric acid; crystals of glycocholic acid are slowly deposited. This substance, however, is not pure even yet, for a part only of these crystals is soluble in water, scales of a body isomeric with glycocholic acid being left; this insoluble portion has been termed paracholic acid by Strecker. If paracholic acid be dissolved in alcohol, the addition of water precipitates it in the form of crystals of glycocholic acid.

241 39

(1694) Cholic Acid of Demarçay, Cholalic Acid of Strecker; (HЄH,H2, and 24 H,O); Fusing pt. 383° (195° C.).—By Ꮎ . adding hydrochloric acid drop by drop to the solution of baric cholate obtained by boiling glycocholic acid with baryta, the cholic acid is separated as a resinous mass; and this, on adding a small quantity of ether, is converted into colourless tetrahedra or octohedra, which are brittle and efflorescent. Cholic acid is very slightly soluble in water, forming with it a solution which distinctly reddens litmus. It is however freely soluble in alcohol, but less soluble in ether. The ethereal solution deposits the acid in rhombic tabular crystals which contain H2O; this water of crystallization may be expelled by a gentle heat, after which the acid fuses at 383°, and a little beyond this it loses its basic water, and becomes converted into choloidic acid, and by a still further heat, into dyslysin (1695).

The cholates of the alkali metals and of barium are soluble in water and in alcohol; most of them may be crystallized from their alcoholic solution. The most characteristic test for cholic acid is furnished by treating it with sugar and sulphuric acid; an intense red colour, passing into a violet, is thus developed. Pettenkofer, to whom this observation is due, has founded upon it an excellent test for the presence of bile in organic fluids; cholic acid is formed by the action of the sulphuric acid upon the resinoid acids of the bile, and then furnishes the reaction in question. In order to apply this test, an alcoholic extract of the substance for examination is prepared, and dissolved in water; a drop of syrup consisting of 1 part of sugar to 4 of water is then added, and pure

886

CHOLOIDIC AND TAUROCHOLIC ACIDS.

sulphuric acid free from sulphurous acid is cautiously poured in; the liquid at first becomes turbid, but it clears as more acid is added, and passes in succession through cherry red, carmine, and purple into violet. The temperature must not be allowed to rise beyond 120° or 130°, and care must be taken not to use too much sugar, or it would be liable to become charred by the sulphuric acid. Acetic acid may be substituted for the syrup in applying this test. Cholic acid approaches the fatty acids in character, and its salts are somewhat analogous to ordinary soaps.

(1695) Choloidic Acid (H7).-Glycocholic acid is soluble in cold concentrated acetic, sulphuric, and hydrochloric acids without alteration, but it is decomposed when heated with them. If glycocholic acid be boiled with hydrochloric acid, glycocine is separated, and a new resinous acid, the choloidic of Demarçay, is produced :

Two atoms of cholic acid, by the abstraction of the elements of one atom of water, furnish one atom of choloidic acid.

Choloidic acid is a resinous, white, friable substance, freely soluble in alcohol, scarcely soluble in ether, and insoluble in water. It reddens litmus, and when treated with sulphuric acid and sugar produces the same reactions as cholic acid. The alkaline choloidates are soluble in alcohol and in water, but they do not crystallize: baric choloidate is insoluble in water. These salts are isomeric with the cholates, but do not at all resemble them. Choloidic acid is stated to contain no basic hydrogen, but this is not probable.

n

2

Both cholic and choloidic acids, like oleic acid, when distilled with nitric acid yield, by oxidation, the volatile fatty acids of the group H; acetic, butyric, caproic, œnanthylic, caprylic, pelargonic, and capric acids having been discovered in the results of the distillation by Redtenbacher. Various other oxidized products remain in the retort, among which are oxalic and cholesteric acids (1700), and a crystallizable body termed choloidanic acid (¤16H2407).

By long boiling with hydrochloric acid, the choloidic acid in turn is decomposed; each atom loses 3 more atoms of water, and becomes converted into a neutral resin (H) fusible at 284° (140° C.), and which, from the difficulty of bringing it into solution by ordinary solvents, Berzelius called dyslysin (from dùs, difficult, Avous, solution).

(1696) Taurocholic Acid; Choleic Acid of Strecker (HЄHNO,S).-The sulphuretted acid of ox bile is the less