these bodies are not pigmented leucocytes, but are really dead and breaking-down parasites; for if the preparations were made within two or three hours of death—— that is to say, when the tissues were quite fresh ——it may be possible to see that the capillaries of some of the organs are full not only of hæmozoin but also of parasites, a very large proportion of the blood corpuscles containing them. Particularly is this the case with the spleen and bone marrow; often, too, with the brain, liver, epiploön, and intestinal mucosa. The spleen and bone marrow are further distinguished from the other organs mentioned by the position in which the hæmozoin occurs in them. In all organs the pigment is found in the blood-vessels, but only in these two organs is it found in the cells of the parenchyma as well, and outside and away from the blood-vessels. This extravascular pigment is either free, or it lies in the large cells characteristic of these organs, or in the small cells of the parenchyma.
Nature and source of malarial pigment.—— In colour, in structure, and in chemical reaction this pigment corresponds exactly with the pigment already described as forming so prominent a feature in the malaria parasites themselves. Like this, it is insoluble even in strong acids; it is altered by potash, and is entirely and rapidly dissolved by ammonium sulphide. In recent infections it occurs as minute dust-like grains; in infections of some standing as coarser particles, or as agglomerations of these into irregular, mammillated lumps. So far as the circulation is concerned, such a pigment is found in no other disease whatever. As an extravascular pathological product a similar pigment is found in certain melanotic tumours; but only in the cells of the tumour, never in the blood-vessels. Pigments of several kinds are found in old blood-clots; but such pigments are manifestly different from that of malaria, and yield very different chemical reactions. Intravascular black pigment, therefore, is absolutely pathognomonic of malaria.*[1] Because of
- ↑ * The pigment-like dot occurring in a large proportion of the lymphocytes in normal blood (see p. 38) must not be confounded with malarial pigment.
