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The ash, moistened with chlorhydric acid and tested with potassic ferrocyanide, reveals very distinctly the presence of iron.
The ultimate analysis of 100 parts of the dried pigment gave
The quantity of oxygen present is very close to 40 per cent. The ash has not yet been analyzed, nor has the presence of sulphur and phosphorus been verified.
The comparative composition of 100 parts of this substance and melanin, disregarding the inorganic matter, is here shown
Thus melanoidin differs from melanin mainly in containing less carbon and more oxygen, that is, it is not so highly vitalized in its composition, and we know that while melanin is a physiological product, our pigment is a pathological one. Compared with urea and uric acid, which contain
we find our pigment much lower in the scale of organic material than either.
The statement has been ventured that this deposit is nothing but “modified hæmatin,"or, speaking in a manner more safely indefinite, "altered blood.” Now aside from the fact that we have no satisfac. tory evidence that hæmatin ever exists ready formed in the blood of vertebrates, the composition of this product, as well as that of other parts and products of the blood, must necessarily preclude any such ventures of opinion, as the following figures (discarding fractions) will show:
Properties.-In its deportment with reagents, melanoidin bears considerable resemblance to melanin. It is insoluble in water, alcohol, ether, chloroform, glycerine, and the dilute mineral acids, as well as in saline solutions generally. It is quickly decomposed and dissolved in strong nitric acid, but insoluble in dilute sulphuric acid with alcohol; solution of potash dissolves it with liberation of ammonia; soluble in sodic hydrate, and also to some extent in cold, strong aqua ammoniæ; dilute aqua ammoniæ softens the dried mass to a soft readily compressible, jelly-like consistence suitable for microscopic study, in which condition a few blood-disks have been observed. These, as well as a few epithelial scales that bave also been found, are no doubt accidentally present. Solutions of the alkaline carbonates do not dissolve it to any considerable extent. Strong, hot solutions of the alkaline chlorides exert a slight bleaching and disintegrating effect, but do not dissolve it appreciably. Solution of chlorate of potassa has the same effect to a more marked extent. Solution of chlorate of potassa with chlorbydric acid (producing liberation of euchlorine) quickly bleaches it to a pearly whiteness, and slowly dissolves the greater portion of it. Long. continued treatment with euchlorine effects its complete decomposition and solution. Unlike melanin, it is not precipitated from its potash solution by chlorhydric acid. Insoluble in fixed and volatile oils. Insoluble in solution of urea and in bisulphide of carbon.
Microscopic and Spectroscopic Appearances.-Sections of pigmented skin and a potassic solution of dried pigment (from case 1st) have been submitted, the former to microscopic and the latter to spectroscopic examination, with the following results.
The integument was first dried to a degree sufficient to make the cutting of sections an easy operation, and sections then made perpendicular to the surface of the skin. The pigment, which was deposited mainly in the cutis vera, was found in minute granules of almost constant size, namely 36ooo of an inch in diameter, and roughly spherical in form. It seemed to pervade, alike, any and all parts of the true skin, being, however, most plentiful in the
I Not determined.
middle portions. Glycerin, and also dilute aqua ammoniæ, render it almost invisible by giving it a light-brown transparency difficultly distinguishable from the skin itself. When thus treated the granules swell up and coalesce, without, however, showing any evidence of their ever having been blood disks. The appearance of the deposit as thus seen is very different from ordinary extravasations. It is very desirable that the identity of the pigmentary matter of the skin and that from the kidneys and bladder be carefully tested. From the very little that has been determined it would seem that the renal and vesical deposit is less soluble than that of the skin.
The spectrum of melanoidin differs essentially from that of blood or any of its separate proximate elements, either recent or dried ; for, while the absorption bands of bæmaglobin are located near the D line, and near the yellow border of the green in arterial, and between the yellow and the green in venous blood, and while the spectrum of oxidized bæmatin with its three bands, and that of the deoxidized compound with its two bands, are distributed also over the same region of the spectrum, but occupying a greater extent, we find, in the case of melanoidin, no absorption near the red end, and no light transmitted beyond the yellow. So that the spectrum of melanoidin is simply a band of red bordered with yellow light.
Its very limited range of solubility affords but little promise of successful treatment of the cases in which it occurs. The fixed alkalies and their chlorides and chlorates, assisted by chlorhydric or nitric acid, or aqua regia, may act beneficially if they can be administered in sufficient quantity. Ferruginous and other tonics, and perhaps stimulants also, may assist in preventing the formation of the deposit, but would not be likely to aid in its elimination after having been once formed.
Where is it formed ? and by what influence ? are questions of physiological chemistry that must be answered, if at all, after patient and thorough investigation, both chemically and microscopically, of all parts of the circulation and excretory system. From what has been learned, it is probably safe to say, that, if it be not a cryptogamic growth, it has its origin (in a soluble form) before it enters the urinary excretion, and that in entering the same, or before doing so, it passes into an insoluble form.
J. B. HOUGH, M.D., Prof. Chemistry and Toxicology, Miami Medical College, Cin., 0. VOL. XXVI.-15