Pathological data completely confirm this view. Ehrlich at least, in an enormous number of cases, has never once succeeded in confirming the existence of a purely splenic form from the blood examination[33]. The conditions in myelogenic leukaemia are quite similar, for foci of myeloid tissue may appear in the spleen or lymph glands according to the kind of metastasis. As it is the proliferation of the myeloid tissue and not the accompanying swelling of spleen or lymph glands that is specific in the process, the nomenclature "lienomedullary or medullary-lymphatic" leukaemia must also be described as illogical and misleading. We distinguish then, from the histological standpoint, but two forms of leukaemia: 1. =leukaemic processes with proliferation of lymphoid tissue=: "~lymphatic leukaemia~"; 2. =leukaemic processes with proliferation of myeloid tissue=: "~myelogenic leukaemia~." The accompanying clinical phenomena may be indicated by simple unequivocal amplifications, for instance, "lymphatic leukaemia with enlargement of the spleen or of the liver"; "myelogenic leukaemia with enlargement of the lymph glands," &c. From our present knowledge, which, it may be remarked, is still far from full, we may assume that lymphatic and myelogenous leukaemia have quite a different aetiology. The recent discovery of Loewit should be decisive on this point, for he demonstrated in myelogenic leukaemia the presence of forms like plasmodia within the white blood corpuscles, but was unable to find them in lymphatic leukaemia. The necessity of separating lymphatic from myelogenic leukaemia is further shewn by the fundamental clinical differences between them. ~Lymphatic leukaemia~ falls clinically into two readily distinguishable forms. In the first place acute lymphatic leukaemia, characterised by its rapid course, the small splenic tumour, the tendency to petechiae and to the general haemorrhagic diathesis. By its startling course this disease has given all observers the impression of an acute infectious process.