The kidneys rarely show evident pigmentation macro scopically. Still, cases occur in which the cortical substance is dotted with gray points, and the vessels of the pyramids are indicated by gray lines.
The pigmentation is readily recognized microscopically, especially in the glomeruli, where it may be marked. The pigment is found in the glomerular endothelium and in large leukocytes that obstruct more or less the lumina of the vessels.
The endothelium of Bowman's capsule is in places desquamated. The epithelium frequently shows cloudy swelling, and here and there, especially in the convoluted tubules, necrosis. More or less pigment may be found in the uriniferous tubules.
In blackwater fever the kidney changes are marked. The organs are usually enlarged and softer in consistence; in color they are frequently pale and anemic, though again dark red and congested. On the surface are scattered small brownish flakes, the result of diffuse pigmentation of the uriniferous tubules. As first pointed out by Pellerin, the great majority of cases show wedge shaped, hemorrhagic foci with bases which may be several centimeters square toward the surface and apices toward the medulla. Pellerin observed these foci only in the cortex, and never in the columns of Bertini or in the pyramids. In addition to these recent lesions, he called attention, too, to older cystic cavities situated in the cortex and filled with a dark cloudy fluid. It is doubtful whether these areas, which Pellerin regarded as hemorrhages (apoplexie renale), are not, rather, infarcts. Their form supports this last view, though positive hemorrhages do occur in the pyramids (Kelsch and Kiener, O'Neill).
Microscopically, the kidney epithelium shows a diffuse yellowish and granular pigmentation, with here and there desquamation. Casts, fine granular yellowish pigment, and dark amorphous masses are frequently encountered in the uriniferous tubules. Signs of beginning nephritis are sometimes present.
The renal hemorrhages or infarcts are not exclusively characteristic of blackwater fever. They were observed by Laveran in a case of bilious malaria , with several days' anuria. They vary in number and size, sometimes only a few very small ones being present. Moreover, cases of blackwater fever have been reported without hemorrhages (Wheaton). The relation of these to hemoglobinuria is discussed in the section on Pathogenesis.
Macroscopic changes are at most slight, and may be absent.
The most interesting lesions are the occasionally observed swelling of the solitary follicles and Peyer's patches in the ileum and hemorrhagic erosions. The signs of gastro intestinal catarrh are especially frequent in blackwater fever.
Microscopically, the capillaries of the intestinal villi commonly show more or less pigment.
In one case of choleraic pernicious Bignami found macroscopic ally intense injection of the stomach and intestinal mucous membrane and numerous punctate hemorrhages; microscopically, enormous numbers of parasites in the capillaries, and wide spread necrosis of the epithelium. Barker has also found the capillaries of the gastric mucous membrane filled with mononuclear macrophages containing parasites, together with small circumscribed necroses of the mucosa as a result of the occlusion of the vessels by these cells. It is very probable that systematic examination of the mucous membrane of the digestive tract would demonstrate these findings as not uncommon.
The peritoneum rarely manifests alterations. Laveran observed in one case small punctate hemorrhages.
In the lungs, apart from occasional lobular pneumonic areas or infarcts, no macroscopic changes are noticeable. Microscopically, the alveolar capillaries are found filled with infected blood corpuscles and macrophages.
According to Colin, Griesinger, and others, the heart muscle is often pale, flabby, and shows fatty degeneration. We have already mentioned Vallin's investigations in reference to the degeneration of the cardiac and voluntary muscles. We may add that Kelsch and Kiener and Laveran attributed the pallor of the myocardium to the general anemia, and were unable to confirm the microscopic findings of Vallin. It is scarcely necessary to state that the vessels of the muscles, similarly to those of the general organism, show red blood corpuscles inclosing parasites.
Ecchymoses of the myocardium and pericardium have been occasionally observed. The bone marrow is brownish red, soft, almost diffluent. In the vessels we find numerous adult and sporulating parasites, as well as crescents, outside the vessels; macrophages, frequently showing signs of degeneration. The nucleated erythrocytes seen, sometimes in large numbers, contain no parasites.
As a result of the attraction which the capillaries of the brain cortex have for the infected erythrocytes the melanosis of this organ is striking. In but few cases of fatal acute malaria is the macroscopic pigmentation wanting. Yet the spinal cord is pale, and shows only here and there grayish brown lines, marking out the pigment containing vessels. The two substances of the spinal cord behave similarly to the corresponding ones of the brain.
Microscopically, the pigment granules in the capillaries of the cortex are sometimes regularly distributed; again, scattered. In the former case we see an extremely pretty outlining of the vessels. This pigment is found in parasites which, on their side, are contained in blood corpuscles. On cross section we find the infected erythrocytes along the vessel walls, the healthy ones in the middle of the stream (Plate VII, Figs. 38 and 39). Pigment is also found in the leukocytes and endothelium. The latter is frequently swollen and gives rise to disturbances of circulation. The swelling of the endothelium of the brain capillaries and the occlusion of their lumina by colorless corpuscles (probably parasites) were discovered by Afanassiew.
The finer vessels are not rarely thrombosed by the infected erythrocytes. This appears to be due to a certain adhesiveness of these blood corpuscles. More rarely we find other thrombi caused by the accumulation of free pigment, melaniferous leukocytes, and spores.
The parasites found in the brain capillaries are usually advanced in development; in fact, the majority are often in the act of sporulation. Crescents occasionally occur in great numbers. In the larger vessels the younger forms predominate.