is best isolated from bile in the following manner. Fresh bile is treated with neutral acetate of lead, which precipitates colouring matter, mucus, and cholate of lead. By the addition of a little basic acetate of lead, the cholic acid is more completely precipitated. Cholinic acid is now precipitated from the filtrate by basic acetate of lead and ammonia. The precipitate, after decomposition by hydrothion (sulphuretted hydrogen), yields uncombined cholinic acid. It has an acid reaction, a bitter and sweet taste; when the solution is evaporated, it decomposes, so that the residue becomes partially insoluble. It is less changeable when in combination with alkalies; and the solution of such salts may be evaporated at a boiling heat. The watery solutions of these salts froth like soap-water; no metallic salt forms a precipitate with them the sole exception being basic acetate of lead, and even that does not precipitate the whole of the acid.

When treated with caustic alkalies, cholinic acid is decomposed; cholalic acid and taurine being the products.

C2H45NO14S2 + 2HO = C4H40010+ C4H,NO¿S2.

Cholinic acid.

48

Cholinic acid, therefore, has a constitution analogous to that of cholic acid; the difference consisting in the replacement of glycocoll by taurine.

Taurine, C,H,NO,S2, may be easily obtained from bile by boiling it with hydrochloric acid for some length of time. The fluid is filtered from the precipitate of dyslysine, evaporated, and mixed with spirits of wine, whereby taurine is precipitated; chloride of sodium and hydrochlorate of glycocoll remaining in solution. Taurine crystallizes in large monoclinometric prisms; they are colourless, transparent, little soluble in cold, easily soluble in hot water, insoluble in alcohol and ether. No other combinations of this body are known; but a key to its composition has lately been obtained by Strecker, who succeeded in producing it artificially, simply by exposing isæthionate of ammonia to a temperature of 220° C. (428° F.) The loss of two equivalents of water transforms this salt into taurine.

If we compare with this result the experiment of the decomposition of taurine by fusion with hydrate of potash, where ammonia and hydrogen are evolved, sulphurous and acetic acids remaining in combination with potash, we have a most remarkable instance of the arrangement of elements round certain nuclei or radicals. The formula of the decomposition of taurine by potash is

CH,NOS2+3KO + HO=

Taurine.

KO. CHO2+ 2(KO. SO2) + NH3+ 2H.

Acetic acid.

Isæthionate of ammonia is

NHO. CHÃO. 2SO3

Oxyde of Ethyl.

=

(C4H,NO8S2).

We find the oxyde of æthyl oxydized at the expense of the oxygen of water and sulphuric acid, the radical acetyl CH being formed from the radical æthyl. Two equivalents of hydrogen are thereby displaced, and finding all the available oxygen taken up by the oxydation of acetyl (to the hydrate of its oxyde, or aldehyde, lastly to its acid), go away uncombined. Two equivalents of oxygen from the two equivalents of sulphuric acid unite with the oxyde of acetyl, CHO, forming acid of acetyl, or acetic acid, CHO, which remains in combination with the alkali.

Colouring matter of Bile.'

The nature of the colouring matter of bile is very little known. It may be removed from its solution by animal charcoal. The alkaline solution of ox-bile is precipitated by means of baryta-water, or chloride of barium, as long as the precipitate has a purely green colour; the precipitate is then decomposed by means of hydrochloric acid, the fatty acids are removed by means of a little ether. A substance remains, which has been termed biliverdine, and is somewhat analogous to chlorophyll. When heated with nitric acid,

Strecker, loc. cit., p. 376.

it becomes successively blue, violet, and red. This test is to a certain degree characteristic. When the alcoholic solution of bile is exposed to the influence of atmospheric air, the green colouring matter is transformed into a red one, which has a great similarity to the red colouring matter of blood.

When the inspissated residue of ox-bile is extracted with alcohol, there remains, beside mucus, a brown colouring matter, which is soluble in warm dilute spirits of wine, and is precipitated from this solution by alcohol. When dried, this body becomes of a bright, burning yellow colour, and hence has been termed bilifulvine. It is easily soluble in water, on combustion leaves carbonate of soda and lime, and for this reason appears to be the salt of an organic acid.

Diagnosis of Biliary matters in Urine.

It is not probable that biliary matters should occur in urine unaccompanied by colouring matter, though the latter frequently occurs unaccompanied by any of the acids or their salts. The brown, yellowish or reddish-brown colour of urine will therefore generally lead to a suspicion of the presence of biliary matters: the diagnosis may be positively established by the necessary tests.

The best and simplest test for biliverdine is the following. A thin layer of the urine to be tested is spread over a white china plate, and a drop of nitric acid, containing some nitrous acid, is placed in the centre of the circle. If biliverdine be present, the margin of the drop of nitric acid will cause a blue colour to appear in the next circle of urine; the blue circle enlarges towards the circumference of the plate, and the circle next to the drop of nitric acid assumes a violet colour. The blue and violet circles expand, and an inner red circle appears. The test is now completed. The discolorations to yellow and brown which follow are neither constant nor characteristic.

Most precipitates from bilious urine are strongly coloured. But to use the coloration of albumen, for example, as a test for biliverdine, possesses no advantage over the nitric acid colour-test; as, where the amount of colouring matter is so small as not to be indicated by the colour-test, it possesses no practical significance.

Both cholic and cholinic acids have been observed in the urine in a few instances. But they have been sought after so very seldom, that it cannot at present be said whether their occurrence is actually rare. Evidence of their presence is

obtained in the following manner. The urine is evaporated almost to dryness, and the residue extracted with alcohol. The alcoholic solution is again evaporated; the residue is dissolved in a little water, and placed in a white Berlin china dish floating on cold water. A few drops of a solution. of sugar are now intimately mixed with the solution in the china dish; and to this mixture concentrated sulphuric acid is added in drops. When biliary acids are present, the solution at first becomes a little turbid, then clears, becomes then of a pale cherry red, then pink, crimson, and at last of a saturated purple violet. Of course the intensity of these colours depends upon the quantity of biliary acids present, and upon the care which is bestowed upon keeping the temperature of the mixture as low as possible during and after the addition of sulphuric acid. This reaction bearing, from its discoverer, the name of Pettenkofer's test, is due to the presence of cholalic acid, as neither taurine nor glycocoll exhibit it when isolated.

Pathological indications.

The occurrence of the colouring matter of bile in the urine indicates that the flow of bile from the liver into the intestinal canal is impeded or entirely suspended. By absorption the colouring matter of bile enters the blood, and hence passes into all the secretions and tissues. Icterus, as this state of things has been termed, is as easily diagnosed by the coloured tissues and colourless fæces, as from the brown urine, and its reaction with nitric acid.

There is, however, a certain dissolution of the blood consequent upon or part of the pathological process of pyæmia, which produces the green or yellow icteric colour of the skin and tissues, without being accompanied by retention of bile; as the frequent fluid evacuations contain abundance of green colouring matter, and the dark-red or brown urine does not show the colour-test with nitric acid. The analysis of the urine distinguishes these cases from true icterus.

In yellow fever the urine is very rarely impregnated with biliary colouring matter.

The occurrence of cholic and cholinic acids in the urine indicates that these substances, after their secretion by the liver and resorption into the blood and chyle, have not undergone those changes, at present unknown, to which under ordinary circumstances they are subjected in the blood

See also Lehmann, Physiol. Chemie,' vol. ii, p. 209.

or tissues. The appearance of these acids in the urine would therefore indicate either the existence of an abnormal process in the blood, preventing the normal consumption of biliary acids, the liver continuing materially sound and secreting the ordinary bile; or it would indicate an excessive activity of the liver, by which more biliary acids are secreted than the blood and tissues can disintegrate, in consequence of which a part passes into the urine. The experiments of Frerichs 1 seem to show that a very large excess of cholates and cholinates in the blood would be required to make them appear in the urine. For when large quantities of filtered bile were injected into the veins of dogs, the bile disappeared in the blood without leaving traces anywhere, and without causing symptoms. In one case only, where a large quantity of a concentrated solution of pure cholate and cholinate of soda had been injected, a part of it could be discovered in the urine.

Wien. Med. Wochenschrift,' iv, No. 30.