The Pigment may, independently of any development out of extra-vasated blood, be brought about through -

1. The obliteration of small bloodvessels or capillaries, with the conversion to pigment of their contained blood, just as the stain is produced in plugging blood-clots within the greater vessels. As the vessel's parietes disappear through absorption, striated accumulations of pigment corresponding to the course of the vessel, are entailed in the textures. This takes place more particularly in membranaceous areolar tissue formed upon serous membranes previously vascularized. In these the opportunity sometimes offers of tracing the aforesaid process. Even the pigment in callosities entailed by so-called capillary phlebitis may be partly brought about by the same means, namely, by metamorphosis of the blood-coagulum in the vessels destroyed.

2. Through conversion to pigment of the blood in different blaste-mata, especially the products of inflammation and cancer melanodes.

3. By transformation of the blood-pigment along with other substances in the normal act of nutrition, or in consequence of hyperemia and inflammation. The probability of this event will be relative to the predominance of the blood-corpuscles in the circulation generally, to the number of old and very highly colored globules present, and lastly, to the extent to which their coloring matter is taken up by the plasma when attenuated through the diminution of its salts, or the destruction of its fibrin. In this manner it is intelligible how pigment may become engendered without the extravasation of blood-corpuscles, how it so often becomes deposited in the lungs, as the central receptacles for venous blood, how the aged are peculiarly prone to its deposition, and lastly, how in certain crases, the typhous for example, it so frequently attaches, as the residue of hyperemia and inflammation, to the follicular apparatus and the mesenteric glands.

It would seem to have arrived at certain organs partly through resorption - the bronchial glands, for instance.

Our own investigations concerning the morphological process of pigment formation have led to the following conclusions:

The pigment differs according as its basis consists of haematin alone in a state of solution, or of blood-corpuscles.

In effusions reddened by dissolved haematin, the pigment separates as a result both of the changes produced by resorption, by the accompanying menstrua, and by consolidation, and also of probable external agencies effecting coagulation or precipitation in the shape of a granular mass (of discrete or agglomerated molecular granules), which imparts a brown, a yeasty, or black coloration.

Where blood-corpuscles are actually present, either these become dissolved, and the development of pigment out of the coloring matter takes place as in the foregoing case; or else the haematin becomes pigment within the blood-corpuscles, which thereby become transformed into mulberry-shaped corpuscles. These remain separate, or cohere in groups of two, three, or four, or they may even gather together into a lobulated mass. Earlier or later they break up into the molecular pigment-granules before adverted to. Under both forms and modes of development the pigment is, to a greater or less extent, contained in cells. Upon this point, experience has shown us that -

1. Pre-existent nucleated cells (of various forms) take up haematin, which, as the contents of the cells, becomes molecular pigment. This is, perhaps, a repetition of the process that takes place in normal pigment formation.

2. One or more mutually coherent blood-corpuscles constitute, as it were, a nucleus-formation, around which a cell-wall developes itself. Even within this cell the nucleus-mass may break up into molecular pigment. The haematin frequently associates itself, dissolved, to the cell's contents, and there coagulates to molecular pigment, whilst the now colorless nucleus-mass (blood-globules) undergoes, probably in its protein contents (globulin), conversion into fat-globules.

3. A cell-wall forms around a conglomeration of molecular granules. These are frequently all concurrent processes, just as happens with pigment formation external to cells. The two former processes are, however, both attested in colored exudates, and most particularly in cancer rnelanodes. In either way, a sort of pigment granule-cell is brought about.

The precise manner in which the conversion of haematin to pigment takes place, is obscure, if not altogether unknown. It cannot be doubted that the haematin undergoes various and considerable changes. Some indications in point are seemingly derived from the conversion of haema-tin into pigment, through the palpable influence of chemical agents, addressed, sometimes to the haematin itself, sometimes to the iron it contains. Strong mineral acids (sulphuric, for instance) introduced from without darken or blacken the blood with which they come in contact. Carbonic acid gas (evolved, along with carbonic oxide gas, out of glowing charcoal) acts in the same manner upon the capillaries when a stream of it traverses the fauces; and a similar influence is exercised by acid secretions generated in the organism itself, as we have seen in alluding to colored softening of the stomach.

Like the blood itself, the kindred spleen-pulp (spleen-corpuscles) suffers the same transformation of its elements. The change of color is here most probably determined through the combination of haematin with different acids, carburet, chloride of haematin, etc.

The very frequent conversion of red hemorrhagic exudates upon the peritoneum into black strata, is most probably founded upon the influence of the intestinal gases upon the haematin. In common with ammo-niacal gas, it is principally the sulphuretted hydrogen of the bowel which, acting (by exosmosis) upon the iron of the haematin, enters with it into a black combination, namely, sulphuret of iron. A similar effect is wrought by phosphuretted hydrogen in abscess and gangrene.

Fertile in results as are the above anatomical data relative to the fundamental principle of pigment, they seem to throw very little light upon the chemical processes by which the conversion of haematin is regulated. The influences adverted to under which haematin blackens, admit of no ulterior application. We are still reduced to the entailed general view of defective decarbonization of the blood, to which the abundance of carbon detected by analysis in the various black substances, certainly adds weight.

But even should the pigment, as Guillot affirms, of the black pulmonary artery, consist of pure carbon, this would in nowise refute our theory, namely, that it is invariably developed out of haematin.

Although russet- and yeast-colored pigment are obviously derived from the same uniform base with black pigment, yet the conditions upon which the existence of this pigment depends are little known, and its composition still less. Thus much is certain, namely, that in color it is susceptible both of deepening into blackness, and of fading into paleness.

Generally speaking, an organ is liable to become the seat of pigment formation proportionately to its vascularity, to its proneness to hyperemia, inflammation, and hemorrhage, and to the extent to which its blood-supply is marked by excess of coloring matter, that is, by the venous character (Venositat).

The resorption of granular pigment is a fact! How this takes place, - how and whereby it becomes adapted for the process, is not known.

In itself pigment is an innocent new growth.

It is still of some importance to inquire what is to be thought of the distinction of pigment into true and false melanosis. Seeing that pigment has, under all circumstances, one and the same fundamental principle (hsematin), and that our knowledge of its workings is limited, the distinction seems supererogatory. Which is the true and which the false?

We deem it most advisable to abolish the word melanosis altogether, and to substitute for it the term pigment, designating all growths, normal or pathological, into whose composition pigment enters, as pigment-holding or pigmental, and what has been called malignant melanosis, as pigmental cancer, or cancer melanodes.