The conditions in myelogenic leukæmia 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" leukæmia must also be described as illogical and misleading.
We distinguish then, from the histological standpoint, but two forms of leukæmia:
1. =leukæmic processes with proliferation of lymphoid tissue=:
2. =leukæmic processes with proliferation of myeloid tissue=:
The accompanying clinical phenomena may be indicated by simple unequivocal amplifications, for instance, "lymphatic leukæmia with enlargement of the spleen or of the liver"; "myelogenic leukæmia 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 leukæmia have quite a different ætiology. The recent discovery of Löwit should be decisive on this point, for he demonstrated in myelogenic leukæmia the presence of forms like plasmodia within the white blood corpuscles, but was unable to find them in lymphatic leukæmia.
The necessity of separating lymphatic from myelogenic leukæmia is further shewn by the fundamental clinical differences between them.
~Lymphatic leukæmia~ falls clinically into two readily distinguishable forms. In the first place acute lymphatic leukæmia, characterised by its rapid course, the small splenic tumour, the tendency to petechiæ and to the general hæmorrhagic diathesis. By its startling course this disease has given all observers the impression of an acute infectious process.
The second form of lymphatic leukæmia is marked off from the preceding by its chronic, and often very protracted course. The spleen shews its participation in the disease, as a rule by very considerable enlargement. We have at present no investigations adequate to decide whether chronic lymphatic leukæmia represents a single disease, or should be etiologically subdivided. Hæmatologically, all lymphatic leukæmias are characterised by a great preponderance of lymph cells, in particular of the larger varieties. It should here be expressly mentioned, that richness of the blood in large lymph cells, is by no means characteristic of the acute form of leukæmia, for chronic, very slowly progressing cases shew the same condition. Thus in a case of this kind under observation in Gerhardt's wards, all observers (Grawitz, v. Noorden, Ehrlich) found the large cells during its whole course. In agreement with our remarks elsewhere (see p. 104), we assume with regard to the origin of lymphatic leukæmia, =that the increase of the lymph cells is brought about by a passive inflow into the blood; and not by an active emigration from chemical stimuli=.