We define lymphocytosis as an increase of the lymphocytes of the blood; Fraenkel like Uskoff regards it as the emigration of the young forms of the white blood corpuscles into the blood. He concludes logically from the diminution of the polynuclear cells in this form of disease "that the conditions of the transformation of the young forms have undergone a disturbance." But if one assumes that the lymphocytes are young forms, and the polynuclears their older stages, it is much nearer to the facts to speak, not of a disturbance in lymphatic leukaemia, but of an absolute hinderance to the ripening process. It is easy to conceive any particular stimulus or injury bringing about an acceleration of the normal process, that is, a premature old age, but it is equally difficult to represent clearly to oneself conditions which retard or completely prevent the normal ageing of the elements. The discovery of such conditions would be really epoch-making, both for general biology, and for therapeutics. The only escape from this dilemma would be the assumption of a very premature death of the lymphocytes, for which however not the smallest evidence is to be found, even in Fraenkel's monograph. Fraenkel distinguishes the acute from the chronic forms of leukaemia by the fact, "that in the former the newly formed elements emigrate from their places of formation into the blood-stream with extraordinary rapidity. Hence there is not time for further local metamorphosis. In chronic leukaemia the emigration takes place very probably much more slowly." This distinction is contradicted by the facts; for =there are chronic forms of lymphatic leukaemia whose microscopic picture is identical with that of acute leukaemia=. And hence the starting-point of all Fraenkel's deductions is rendered insecure. FOOTNOTES: [14] C. S. Engel has recently proposed to call acute leucocytosis "=lienal leucocytosis=," in analogy with the clinical idea of a lienal leukaemia. This terminology should only be used if the polynuclear cells did in fact arise from the spleen, an assumption which Engel himself does not once appear to make, since he expressly warns against drawing any conclusions from this name as to their origin. Since, however, the acute leucocytoses, as we shall shew in the next section, are exclusively to be referred to the bone-marrow, the term lienal leucocytosis seems to us quite mistaken, for it must logically lead to a conception of the origin of the leucocytes, exactly opposed to their actual relationships. [15] Many authors, _e.g._ Arnold, explain this double staining of the eosinophil cells by the presence of eosinophil and mast cell granulation side by side. That this is certainly not the case is shewn by the fact that the "basophil" granulation of the eosinophil cells does not in metachromatic staining shew the metachromasia characteristic for the mast cells.