Pigment

The anatomic characteristic of acute malaria is the melanemia.

Macroscopically this is evident in the grayish brown to graphite color of certain organs, as the spleen, liver, brain, and kidneys.

Among the older observers who were struck by this abnormal color of the organs and remarked it, though without recognizing its true basis,-i. e., the melanemia,-we may mention Lancisi, Stoll, Bailly, Billard, Mortfaucon, Richard Bright, and, from still later times, Haspel and Annesley. Lancisi noted once a black, pigmented liver, Stoll the same, together with a similarly pigmented brain, and Bright, in his "Reports of Medical Cases," gave a description of a graphite colored brain.

In regard to the discovery of the malaria pigment by Meckel and Virchow, as well as its physicochemic properties and the views formulated for its origin, we have said sufficient on pages 46 and 231.

Here we intend to consider the distribution of the pigment in the organs. The pigment is free in the blood plasma only in very slight amounts. It is found principally in the parasites (which, on their part, are inclosed in erythrocytes) or in tissue cells. Among the latter we may mention the leukocytes, the macrophages of the spleen, endothelial cells, marrow cells, and, more rarely, parenchymatous cells of glandular organs (liver cells). Among the leukocytes, the polymorphonuclear cells are the most eager scavengers, the lymphocytes playing this role but rarely. Yet isolated instances have been observed, as that of Lewellys Barker, in which the lymphocytes had taken up considerable pigment. Eosinophile cells come on this scene only exceptionally.

The distribution of the pigment in the internal organs-as, likewise, the distribution of the parasites-is not, as a rule, uniform. In the section on the etiology of malaria we stated that the quartan parasites are encountered in the peripheral blood in almost the same proportion as in the blood of the internal organs, while the tertian parasites, and, still more, the parasites of the second group, are found in much larger numbers in the latter, and especially in the blood of the spleen, brain, etc.

As demonstrated by Frerichs, the pigment is found in the capillaries rather than in the larger vessels. Again, among the capillaries, the pigmented parasites show a predilection for a certain few, namely, those of the spleen, liver, brain, and not rarely the kidneys. According to Kelsch and Kiener, they are especially numerous in small vessels, where the caliber of the artery goes over suddenly into the narrow caliber of the capillary, thus producing a slowing of the bloodstream, as, for instance, the capillaries of the lungs, the intestinal villi, the appendices epiploicse, the glomeruli of the kidneys, the dura mater, and the cerebral convolutions. The most common actual sites are the capillaries of the spleen, liver, and brain. Still there are cases in which the distribution deviates from the rule, so that capillary regions which usually show a scanty number of parasites are packed with them, and vice versa-for instance, Frerichs' case, in which the spleen was free, the liver full of pigment, and numerous others in which the capillaries of the gastro intestinal mucous membrane were the seats of predilection.

The factors concerned in this varied distribution of the parasites in different cases are at present unknown to us, just as it is not clear why the parasites are not equally numerous throughout the vascular system, where they reproduce, instead of accumulating in certain organs, as if they were breeding places.

In this respect the malarial parasites behave very differently to dead substances (like powdered glass, cinnabar) introduced into the circulation. These distribute themselves almost uniformly, while the parasites recall the pathogenic bacteria, which, in a similar way, show a predilection for one or another organ.

Let us look at the ordinary distribution of the pigment in the organs. (In this we follow the description of Kelsch and Kiener.)

The Spleen And The Splenic Veins

When death follows a recent malarial infection, we find in the pulp and the venous sinuses of the spleen numerous large mononuclear and polynuclear cells (macrophages), richly laden with pigment. They frequently contain not only pigment, but also parasites (often together with the infected red blood corpuscles) in the earlier stages of development, in the stage of segmentation, and even crescents. Not rarely several parasites are found in one cell, in addition to some free pigment or non infected red blood corpuscles.

Besides the macrophages, the polynuclear leukocytes and lymphocytes may contain pigment, though in relatively small amounts. In this stage the endothelial cells, the lymph sheaths of the arteries, the Malpighian bodies, and the connective tissue stroma are devoid of pigment. Moreover, the arteries contain a much smaller number of pigmented bodies than the veins.

The pigment is found in greatest amount in the splenic vein, where it is seen both in macrophages and in still active parasites.

If a short interval elapses after the acute infection and the patient succumbs to another disease, no parasites will, of course, be found in the circulating blood, and consequently no pigment, while the splenic tissue will be markedly pigmented, and, microscopically, will show this pigment in the pulp, the lymph sheaths of the arterial vessels, and the Malpighian bodies. The pigment is also more clumped, and is frequently deposited in the form of nests.

Liver, Portal Vein, Hepatic Veins

In acute cases the pigment is found in macrophages, as well as in parasites within the portal vein and its capillaries. The splenic macrophages are seen especially adhering to the walls of the portal capillaries, which are sometimes occluded by the enormous numbers. In the hepatic veins pigmented parasites occur, but no macrophages. The liver cells and Glisson's capsule contain no pigment, except when death takes place several days or weeks after the termination of the acute infection.