It is seen that I have taken no notice of {62} 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. {63} _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. [Illustration: 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 {64} 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. [Illustration: FIG. 5. Spiculated balls of tyrosine, from the urine of a case of acute atrophy of the liver. When these were re-dissolved, purified, and re-crystallized, they assumed the form represented in Fig. 4 _(b)_.]