CHAPTER VIII.

THE BILE.

THE bile is more easily obtained in a state of purity than any other of the secretions which find their way into the intestinal canal, owing to the existence of a gall-bladder in which it accumulates, and from which it may be readily obtained without any other admixture than the mucus of the gall-bladder itself. Notwithstanding this, its study has proved an unusually difficult one. This difficulty has resulted from the peculiar nature of the biliary ingredients, and the readiness with which they become altered by chemical manipulation; and it is, accordingly, only quite recently that we have arrived at a correct idea of its real constitution.

The bile, as it comes from the gall-bladder, is a somewhat viscid and glutinous fluid, varying in color and specific gravity according to the species of animal from which it is obtained. Human bile is of a dark golden brown color, ox bile of a greenish yellow, pig's bile of a nearly clear yellow, and dog's bile of a deep brown. We have found the specific gravity of human bile to be 1018, that of ox bile 1024, that of pig's bile 1030 to 1036. The reaction of the bile with test-paper cannot easily be determined; since it has only a bleaching or decolorizing effect on litmus, and does not turn it either blue or red. It is probably either neutral or very slightly alkaline. A very characteristic physical property of the bile is that of frothing up into a soap-like foam when shaken in a testtube, or when air is forcibly blown into it through a small glass tube or blowpipe. The bubbles of foam, thus produced, remain for a long time without breaking, and adhere closely to each other and to the sides of the glass vessel.

The following is an analysis of the bile of the ox, based on the calculations of Berzelius, Frerichs, and Lehmann:

1.34

1000.00

BILIVERDINE. Of the above mentioned ingredients, biliverdine is peculiar to the bile, and therefore important, though not present in large quantity. This is the coloring matter of the bile. It is, like the other coloring matters, an uncrystallizable organic substance, containing nitrogen, and yielding to ultimate analysis a small quantity of iron. It exists in such small quantity in the bile that its exact proportion has never been determined. It is formed, so far as can be ascertained, in the substance of the liver, and does not pre-exist in the blood. It may, however, be reabsorbed in cases of biliary obstruction, when it circulates with the blood and stains nearly all the tissues and fluids of the body, of a peculiar lemon yellow color. This is the symptom which is characteristic of jaundice.

CHOLESTERIN (CHO).-This is a crystallizable substance which resembles the fats in many respects; since it is destitute of nitrogen, readily inflammable, soluble in alcohol and ether, and entirely insoluble in water. It is not saponifiable, however, by contact with the alkalies, and is distinguished on this account from the ordinary fatty substances. It occurs, in a crystalline form, mixed with coloring matter, as an abundant ingredient in most biliary calculi; and is found also in different regions of the body, forming a part of various morbid deposits. We have met with it in the fluid of hydrocele, and in the interior of many encysted tumors. The crystals of cholesterin (Fig. 46) have the form of very thin, colorless, transparent, rhomboidal plates, portions of which are often cut out by lines of cleavage parallel to the sides of the crystal. They frequently occur deposited in layers, in which the outlines of

the subjacent crystals show very distinctly through the substance of those which are placed above. Cholesterin is not formed in the

liver, but originates in the

substance of the brain and nervous tissue, from which it may be extracted in large quantity by the action of alcohol. From these tissues it is absorbed by the blood, then conveyed to the liver, and discharged with the bile.

The fatty substances and inorganic saline ingredients of the bile require no special description.

Fig. 46.

CHOLESTERIN from an Encysted Tumor.

BILIARY SALTS.--By far the most important and characteristic ingredients of this secretion are the two saline substances mentioned above as the glyko-cholate and tauro-cholate of soda. These substances were first discovered by Strecker, in 1848, in the bile of the ox. They are both freely soluble in water and in alcohol, but insoluble in ether. One of them, the tauro-cholate, has the property, when itself in solution in water, of dissolving a certain quantity of fat; and it is probably owing to this circumstance that some free fat is present in the bile. The two biliary substances are obtained from ox-bile in the following manner:

The bile is first evaporated to dryness by the water-bath. The dry residue is then pulverized and treated with absolute alcohol, in the proportion of at least 3j of alcohol to every five grains of dry residue. The filtered alcoholic solution has a clear yellowish color. It contains, beside the glyko-cholate and tauro-cholate of soda, the coloring matter and more or less of the fats originally present in the bile. On the addition of a small quantity of ether, a dense, whitish precipitate is formed, which disappears again on agitating and thoroughly mixing the fluids. On the repeated addition of ether, the precipitate again falls down, and when the ether has been added in considerable excess, six to twelve times the volume of the alcoholic solution, the precipitate remains permanent, and the whole mixture is filled with a dense, whitish, opaque deposit, consisting of

the glyko-cholate and tauro-cholate of soda, thrown down under the form of heavy flakes and granules, part of which subside to the bottom of the test-tube, while part remain for a time in suspension. Gradually these flakes and granules unite with each other and fuse together into clear, brownish-yellow, oily, or resinouslooking drops. At the bottom of the test-tube, after two or three hours, there is usually collected a nearly homogeneous layer of this deposit, while the remainder continues to adhere to the sides of the glass in small, circular, transparent drops. The deposit is semi-fluid in consistency, and sticky, like Canada balsam or halfinelted resin; and it is on this account that the ingredients composing it have been called the "resinous matters" of the bile. They have, however, no real chemical relation with true resinous bodies, since they both contain nitrogen, and differ from resins also in other important particulars.

At the end of twelve to twenty-four hours, the glyko-cholate of soda begins to crystallize. The crystals radiate from various points in the resinous deposit, and shoot upward into the supernatant fluid, in white, silky bundles. (Fig. 47.) If some of these crystals

be removed and examined by the microscope, they are found to be of a very delicate acicular form, running to a finely pointed extremity, and radiating, as already mentioned, from a central

point. (Fig. 48.) As the ether evaporates, the crystals absorb moisture from the air, and melt up rapidly into clear resinous drops; so that it is difficult to keep them under the microscope long enough for a correct drawing and measurement. The crystallization in the test-tube goes on after the first day, and the crystals increase in quantity for three or four, or even five or six days, until the whole of the glyko-cholate of soda present has assumed the solid form. The tauro-cholate, however, is uncrystallizable, and remains in an amorphous condition. If a portion of the deposit be now removed and examined by the microscope, it is seen that the crystals of glyko-cholate of

soda have increased considerably in thickness (Fig. 49), so that their transverse diameter may be readily estimated. The uncrystallizable tauro-cholate appears under the form of circular drops, varying considerably in size, clear, transparent, strongly refractive, and bounded by a dark, well-defined outline. These drops are not to be distinguished, by any of their optical properties, from oil-globules,

Fig. 49.

GLYKO-CHOLATE AND TAURO-CHOLATE OF

as they usually appear under SODA, FROM OX-BILE, after six days' crystalliza

the microscope. They have the same refractive power,

tion. The glyko-cholate is crystallized; the taurocholate is in fluid drops.

the same dark outline and bright centre, and the same degree of consistency. They would consequently be liable at all times to be mistaken for oil-globules, were it not for the complete dissimilarity of their chemical properties.

Both the glyko-cholate and tauro-cholate of soda are very freely soluble in water. If the mixture of alcohol and ether be poured off and distilled water added, the deposit dissolves rapidly and completely, with a more or less distinct yellowish color, according to the proportion of coloring matter originally present in the bile. The two biliary substances present in the watery solution may be separated from each other by the following means. On the addition of acetate of lead, the glyko-cholate of soda is decomposed, and precipitates as a glyko-cholate of lead. The precipitate,