The most important consideration is, whether cells capable of spontaneous movement, and of active emigration into the blood, are increased ("active leucocytosis"); or whether the number of those cells is raised, to which an independent mobility cannot be ascribed, which therefore are only passively washed into the blood-stream by mechanical forces ("passive leucocytosis").
The passive form of leucocytosis corresponds to the different kinds of lymphæmia, including that of leukæmia. In the section on the lymphatic glands, we have established this view in detail, and we have particularly insisted that a suppuration, consisting of lymph cells, does not occur.
In sharp contrast to this form there are for every specific kind of active leucocytosis, analogous products of inflammation (pus, exudations), composed of the same kind of cell.
We divide active leucocytosis into the following groups:
(α) polynuclear leucocytoses:
1. polynuclear neutrophil leucocytosis,
2. polynuclear eosinophil leucocytosis;
(β) mixed leucocytoses in which the granulated mononuclear elements take part; "myelæmia."
α 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 Türk has for the first time established the fact by an abundance of numerical estimations[25].