18 Professor Hoppe tests for bile-acids in the following manner:—The urine is boiled with an excess of milk of lime for about half an hour, and filtered to free it from the precipitate thus formed. The filtrate is evaporated to dryness, decomposed with hydrochloric acid, washed with water, and then extracted with alcohol. The alcoholic extract contains the bile-acids, which are recognised by Pettenkofer's test.
The readiest mode by which the biliary acids may be detected is the following: To a couple of drachms of the suspected urine add a small fragment of loaf-sugar, and afterwards pour slowly into the test-tube about a drachm of strong sulphuric acid. This should be done so as not to mix the two liquids. If biliary acids be present, there will be observed at the line of contact of the acid, and urine—after standing for a few minutes—a deep purple hue.19 This result may be taken as a sure indication that the jaundice is due to obstructed bile-ducts. On the other hand, the absence of this phenomenon, and the occurrence of merely a brown instead of a purple tint, although, in the earlier stages of jaundice, equally indicative of suppression, is of course, for the reasons already given, no indication of the cause of the suppression. That must be gleaned from other circumstances.
19 The immediate formation of a reddish coloured line is due to the acid setting free urohæmatine, the normal colouring matter of the urine.
It is seen that I have taken no notice of Frerichs' theory regarding the bile-acids being changed into bile pigment. I have done so advisedly, feeling as I do, that when that observer investigates the subject more fully, he will himself abandon such an untenable doctrine, founded as it is, on an erroneous view regarding the nature of bile pigment. The colour induced by sulphuric acid on the acids of the bile, is as different in its chemical nature from animal pigment, as any two substances can possibly be. Indeed, they have no bond of connection whatever, except the mere tint. All animal pigments, whether they be green, like bile-colouring matter, or red, like hæmatine, spring from the same source, and contain iron. Besides this, the mere fact of an increase of animal pigment being found in the urine after the bile-acids have been injected into the circulation, to which Frerichs attaches such importance, in reality proves nothing more, as Kühne pointed out, than that an increased destruction of blood corpuscles has taken place. I have found the urine of dogs loaded with dark colouring matter after injecting chloroform, and other stimulants into their portal veins, in order to establish artificial diabetes; and, assuredly, in these cases the presence or absence of bile-acids in the blood had nothing to do with the result.
Diagnostic Value of the presence of Tyrosine, and Leucine in Urine.
There are two other abnormal products occasionally met with in the urine of jaundice, namely, tyrosine, and leucine. These substances, although for many years known to chemists, attracted comparatively little attention until Frerichs discovered their diagnostic value in hepatic disease.
| FIG. 4. |
| Crystals of pure tyrosine, obtained from the urine of a case of chronic atrophy of the liver, following upon obstruction of the bile-duct. (a) Large crystals. (b) The more common form of the stellate groups of needle-shaped crystals. (c) A few separate fragments of needle-shaped crystals. |
In that peculiar form of complaint, described as acute or yellow atrophy of the liver, the urine is said invariably to contain tyrosine, and leucine. The presence of these substances may therefore assist us in diagnosing the case. When tyrosine, and leucine are present in quantity, they are very readily detected, all that is required being slowly to evaporate an ounce of urine, to the consistency of syrup, put it aside during a few hours to crystallize, and then examine it with the microscope. The tyrosine is recognised by being in fine stellate groups of needle-like crystals, as represented in fig. 4, or spiculated balls not unlike a rolled-up hedgehog, with the bristles sticking out in all directions.