1. =polynuclear neutrophil leucocytosis=, 2. =polynuclear eosinophil leucocytosis=; ([beta]) =mixed leucocytoses= in which the granulated mononuclear elements take part; "=myelaemia=." [alpha] 1. ~Polynuclear neutrophil leucocytosis~, is the most frequent of all forms of active leucocytoses. Virchow, the discoverer of leucocytosis, advocated the view, that it resulted from an increased stimulation of the lymph glands. The stimulation of the lymph glands consists in "that they are engaged in an increased formation of cells, that their follicles enlarge, and after a time contain many more cells than before." The swelling of the lymphatic glands has as a consequence an increase of the lymph corpuscles in the lymph, and through this an increase again of the colourless blood corpuscles. This standpoint had to be abandoned, when Ehrlich shewed that it is chiefly the emigration of the polynuclear neutrophil cells, which brings about leucocytosis. Exact figures on this point were first given by Einhorn, who worked under Ehrlich, and were later generally confirmed. Corresponding with the increase of neutrophil blood corpuscles alone, there is always a relative decrease of lymphocytes, often to 2% and even lower. It must here be borne in mind, that the percentage of the lymph cells may be much diminished, without change in their absolute number. It has however been conclusively demonstrated that occasionally in polynuclear leucocytosis, the absolute number of the lymphocytes may decrease. Einhorn had already described a case of this kind, and recently Tuerk has for the first time established the fact by an abundance of numerical estimations[25]. The eosinophil cells are as a rule diminished in ordinary polynuclear leucocytosis, as Ehrlich had already mentioned in his first communication. The diminution is often considerable, often indeed absolute. A few diseases shew, besides the neutrophil leucocytosis, an increase of the eosinophils as well, as we shall describe in detail in the next section. Polynuclear neutrophil leucocytosis--leucocytosis [Greek: kat' exochen]--may be divided into several groups =according to their clinical occurrence=. We distinguish: A. =physiological leucocytosis=, which appears in health as an expression of changes in the physiological state. To this group belongs the leucocytosis of digestion, the leucocytosis from bodily exertion (Schumburg and Zuntz) or from cold baths, and further the leucocytosis of pregnancy. B. =pathological leucocytosis=.