We think then we must draw the conclusion that the feeble mobility of the mononuclear cells, both eosinophilous and polynuclear, is only apparent, and is owing to the gross method of investigation. In reality they doubtless have mobility sufficient for emigration.
A further, but much less weighty objection to the view that myelogenic leukæmia is an active leucocytosis is, that pus artificially produced in leukæmic patients has nearly always the histological constitution of normal pus. But from our previous detailed remarks we should only expect a myelæmic constitution of the pus, if the specific morbid agent of leukæmia were present in a concentrated form at the place of inflammation. Just as we saw in pemphigus, Neusser's eosinophilous suppuration occurred only in the specific pemphigus bullæ, but not in the foci of suppuration that were artificially produced. We know that the myelocytes are in no way positively influenced by the chemiotactic stimuli of ordinary infectious agents. On the contrary, it clearly follows from the above-mentioned observations on the transformation of leukæmic blood under the influence of infectious diseases, that the common bacterial poisons act in a negatively chemiotactic sense, both on the eosinophil and on the neutrophil mononuclear cells. Under these circumstances we should indeed expect that artificially produced suppuration in leukæmic patients would have, not a myelæmic, but a polynuclear neutrophil character.
It will be the task of further investigations to examine accurately inflammatory products, _e.g._ pleuritic exudations, in leukæmic patients, with the object of elucidating the question, whether under special conditions of disease all the leucocytes characteristic for leukæmia may not be able to wander from the blood. Thus in a case of pleurisy in a leukæmic patient, Ehrlich received the impression from the preparations that a "myeloid" emigration had in fact occurred, carrying all the elements in the blood into the exudation. This observation does not prove the point, for numerical estimation of the proportion of white to red blood corpuscles in the exudation was not made. And these estimations are necessary in order to prove indisputably the active emigration of the white blood corpuscles into the exudation, and to exclude their purely mechanical passage, _per rhexin_, from the blood-stream.