The parasite, commonly known as the Leishman-Donovan body, is intracellular (fig. 50, 2, 3). It is found in the endothelial cells of the capillaries of the liver, spleen, bone-marrow, lymphatic glands and intestinal mucosa, and in the macrophages of the spleen and bone-marrow. Some host cells may contain many parasites. It is rather rare in the circulating blood, but may be found in the blood from the femoral, portal and hepatic veins. It does not occur in the red blood corpuscles as was formerly thought. The parasites liberated from the endothelial cells are taken up by the mononuclear and polymorphonuclear leucocytes. The Leishman-Donovan body is the resting stage of a flagellate. As found in man it is a small, oval organism, about 2·5 µ to 3·5 µ in length by 2 µ in breadth, and containing two chromatinic bodies, corresponding to the nucleus and kinetic nucleus (blepharoplast) of a flagellate. The latter element is the smaller and more deeply staining, and is usually placed at the periphery, transversely to the longer axis of the oval organism. There is sometimes a very short, slightly curved filament to be seen, which may be a rhizoplast. Multiplication takes place by binary or multiple fission. The presence of the parasite used to be demonstrated by splenic or hepatic puncture; nowadays it can be demonstrated in peripheral blood, _e.g._, of the finger, or by culture of infected blood. [Illustration: FIG. 50.--_Leishmania donovani_. _1_, Free forms, each with nucleus and rod-shaped blepharoplast (after Christophers); _2_, endothelial cell and leucocytes containing parasites (after Christophers); _3_, capillary in the liver showing endothelial cells containing parasites (after Christophers); _4_, two parasites escaping from a leucocyte in the alimentary canal of the bug (after Patton); _5_, further development in bug (after Patton); _6_, young flagellate forms in bug (after Patton); _7_-_11_, culture forms (after Leishman); _7_, _8_, _9_, show development of flagellum.] _L. donovani_ can be cultivated in citrated splenic blood, under aerobic conditions, at 22° to 25° C. This was first accomplished by Rogers (1904). It is not so easily culturable as _L. infantum_ on the Novy-MacNeal-Nicolle medium.[124] _L. donovani_ is inoculable with some difficulty into experimental animals--in India, white rats, white mice, dogs and monkeys (_Macacus spp._), have been inoculated. The Sudan variety, somewhat less virulent, is inoculable to monkeys. Row also produced a local lesion in _Macacus sinicus_ by subcutaneous inoculation of _L. donovani_. Parasites taken from such a local lesion were found to be capable of producing a generalised infection in _Macacus sinicus_ and white mice. [124] For the composition of this medium, see Appendix.