The pathological pigmentation of the body results, presumably, from the metamorphosis of the coloring matter of the blood or from the introduction from without of pigments insoluble in the fluids of the body. The former of these methods has recently been studied by Langhans39 and Cordua,40 and the present views of this subject are chiefly due to their observations, as well as to the earlier investigations of Virchow and others.
39 Virchow's Archiv, 1870, xlix. 66.
40 Ueber Resorptionsmechanismus von Blutergüssen, Berlin, 1877.
The hæmoglobin contained in red blood-corpuscles is considered to be composed of a coloring matter, hæmatin, combined with an albuminate, globulin. When blood is removed from the body the hæmoglobin is readily separated from the corpuscles by various agents, and is then dissolved in the plasma, which becomes lac-colored. This solubility of the hæmoglobin is of importance in connection with the absorption of extravasated blood. During the time necessary for this process to take place, observable changes are apparent in the color of the affected part when its seat is superficial, especially cutaneous. These changes in color are largely dependent upon the modifications undergone by the hæmoglobin.
It is well known that a yellowish discoloration of the general surface frequently takes place when extensive internal hemorrhages have occurred, constituting a form of jaundice (hæmatogenous) attributed to the presence of the coloring matter of the blood. As yet there has been no satisfactory chemical analysis of this diffused pigment, which if not hæmatin must be regarded as its derivative, although a coexistent increase of the urobilin in the urine has been observed. The association of the stained skin and urine, in the absence of causes favoring an absorption of bile-pigment, leads to the inference that the abnormal discoloration is due to the absorption into the circulating fluids of the body of a pigment dissolved out of the extravasated red blood-corpuscles. This view is confirmed by the microscopic examination of the latter, which discloses the presence of pale, shadowy, round outlines enclosing faintly granular material, which are regarded as decolorized red corpuscles. In the course of a few days glistening crystals and granules of a yellowish-red color make their appearance in the midst of the unabsorbed blood. The crystals are usually oblique rhombic prisms, varying in size from the larger symmetrical shapes to the more minute, apparently granular, forms. Acicular crystals are also to be met with, more yellow than red in color, and are sometimes present in great abundance, although they may be wholly absent. Virchow has applied the term hæmatoidin to these crystals. Owing to the resemblance in the chemical reactions of solutions of hæmatoidin and of the biliary coloring matter, bilirubin, and to the similar crystalline forms of the latter, it has been maintained that the two are identical. Late investigations indicate that solutions of crystals with the appearances of hæmatoidin are not invariably alike in their reaction. A solution of these in chloroform may become decolorized when acted upon by a dilute alkali, or it may not be thus altered. Bilirubin presents the former relation, while chloroform solutions of the coloring matter of the yelk of egg and of the corpus luteum, called lutein or hæmolutein, are not decolorized by an alkali. Although the crystalline forms of hæmatoidin and bilirubin are not to be distinguished, it is not to be conceded that the two substances are identical. As Maly,41 the latest writer on this subject, states, the term hæmatoidin is merely indicative of a microscopical picture. Although the identity of the coloring matter of the blood and of the bile is not admitted, the intimate relation of the two is not only suggested by the similarity of crystalline form, but by the relation determined between urobilin, bilirubin, and hæmoglobin. Urobilin is the coloring matter extracted from the urine in fever by Jaffé, and it has since been obtained from bilirubin by Maly,42 who has given it the name of hydrobilirubin. This hydrobilirubin has also been derived from hæmoglobin. According to Maly, this genetic relation between the coloring matter of the blood and bile, shown in the production of hydrobilirubin, is the only chemical evidence of the connection of the two pigments.
41 Hermann's Handbuch der Physiologie, 1880, vii. 155.
42 Op. cit., 161.
Hæmatoidin is to be regarded not only as directly derived from solutions of hæmoglobin, but as originating through the medium of indifferent cells. Langhans claims that this pigment is formed within movable cells which accumulate in great numbers in the vicinity of the blood-clot, and, in virtue of their amoeboid properties, take into themselves the extravasated corpuscles, entire or in fragments. The indifferent cell may become enlarged into a giant-cell, and then contain numbers of whole or disintegrated red corpuscles. In time these colored corpuscles and fragments become smaller, more glistening, and darker-colored, and eventually are transformed into granular or crystalline hæmatoidin. These granules may be set free by the fatty degeneration of the cell, or may be transferred within the cell to distant parts.
The diffusion and absorption of a solution of hæmoglobin, and the formation of crystals of hæmatoidin from the same or through the medium of cells, are supplemented by an apparent inspissation and condensation of the hæmoglobin. The resulting dark-brown pigment may remain at the seat of the hemorrhage indefinitely, and may be accompanied with reddish-brown flakes, which, as shown by Kunkel,43 are composed of hydrated ferric oxide.
43 Virchow's Archiv, 1880, lxxxi. 381.