(a.) Alteration of hrematosine.— Stagnation and extravasation, and the action of certain chemical agents, are followed by this alteration.
Stagnation produces its etTect on the colour of the blood most distinctly. in the capillary vessels, is more common in old than irr young persons, and attends diseases of the heart and great vessels interfering with the circulation. Chronic inflammation is the most comtnon immediate" cause of the stagnation ; the intes tinal canal and the lung the most common seats of the altered colour. In the intestinal canal, it is difficult (except by ascertaining the absence or presence of acid) to separate the effects of chemical agency from those of rnere stagnation.
Extrava4ated blood (occupying localities altogether removed from the influence of che mical action not originating in itself, as, for example, in the common cellular membrane,) sometimes undergoes remarkable change of colour, becoming of a pitch black hue. The blackish and slaty discolouration frequently seen in points or patches under the raucous coat of the pelvis of the kidney:, and also on the surface of the cortical substance, is evi dently produced by infiltrated and altered blood. In these cases no pigment-cells are to be discovered, an amorphous oranular mass exhibits itself,•not materially differing in phy sical characters (it is not, however, mixed with crystals and fragments of tissue,) from the colouring matter of gangrenous detritus.
Chemical action is a frequent cause of black ening of the blood. Blood poured into the stomach, and sometimes even if retained with in its veins, is blackened by the gastric juice, either by direct contact or by imbibition. The effects of the acid secretion are precisely such as are producible by acids on blood re moved from the body. The slaty discolour ation of the anterior border of the liver, so common an appearance, is similarly explic able ; the blood in its capillary texture being acted upon by hydro-sulphuric acid gas trans uding through the adjacent intestines.
(b.) Introduction of black coloured substances from without. —The lung (with its appen dages) is the only organ in which this source of discolouration has been established. Pear son* was the first to suggest, that inhaled carbonaceous matter was the true cause of the black lines and patches (following the course of the lymphatic vessels) often seen on the surface of the lungs, and of the well known dark hue of the bronchial glands. That
the colouring material was not of animal na ture, he inferred from its being insoluble in nitric acid. Pearson's view seemed to derive support from the well-known dark appearance of the morning expectoration of persons who habitually sit up much at night; and from the observation of Laennec, that the peasantry, but little prone to vigil, rarely expectorate dark sputa.
But the most absolute collateral demon stration of Pearson's correctness, is derived from the history of a peculiar disease to which colliers are subject. The lungs of in dividuals affected with this disease become so thoroughly black (Univ. Coll. Museum) as to resemble coal in colour ; and undergo gradual breaking up from irritative and ulcer ative action.f Now the carbonaceous nature of this material, having been made matter of noto riety by the experiments of numerous persons, it appeared natural to conclude that it was composed of coal dust inhaled in a state of extreme division. This notion was indeed espoused by Dr. J. C. Gregory t, but proved to be erroneous by Professor eraham§, who showed that the material carried into the lung was none other than the soot or lamp-black formed by the combustion of the oil which the colliers use, suspended from their heads, as they work, in mines where the safety-lamp is not used. The constant exposure to the smoke of gunpowder employed for blasting has the same effect, though in a less degree, It retnains for us to add, that we entertain no doubt of the black tint, present always more or less extensively in the lungs and bronchial glands of healthy persons (generally speaking, in the direct ratio of their' ag,es), being in part due to inhaled sooty matter, but believe that it is likewise in part caused by alteration of the hrematin of blood stag nating in the capillary vessels. This opinion 18, however, based on too small a number of micro-chemical examinations to lay claim to general admission.