3. The leucocytosis which accompanies acute and chronic anæmic conditions, especially posthæmorrhagic.
4. Cachectic leucocytosis in malignant tumours, phthisis, etc.[26]
To enter here more precisely into the special clinical importance of blood investigation in different forms of disease would lead us too far, and we refer for this subject to the excellent and thorough monograph on leucocytosis by Rieder and to the papers of Zappert and Türk. In this place we will only touch on the most weighty points.
α. The importance for differential diagnosis of the leukopenic blood condition in typhoid fever as compared with other infectious diseases, and in measles as against scarlet fever.
β. The prognostic importance of the enumeration of the white blood corpuscles. Thus for example the absence of leucocytosis influences the prognosis of pneumonia unfavourably (Kikodse and others); and the appearance of numerous myelocytes in diphtheria is ominous, as demonstrated by C. S. Engel (see page 78).
Finally, we may dismiss in a few words the origin of polynuclear neutrophil leucocytosis, and refer to what has been said in another place on the function of the bone-marrow.
In agreement with Kurloff's researches, Ehrlich formulated ("On severe anæmic conditions" 1892) his views on this subject as follows: "The bone-marrow is a breeding place in which polynuclear cells are produced in large numbers from mononuclear pre-existing forms. These polynuclear cells possess above all other elements the power of emigration. So soon as chemiotactic substances circulate in the blood, which attract the white elements, this power comes into play. This readily explains the rapid and sudden appearance of large numbers of leucocytes, which so many substances bring about, and particularly the bacterio-proteins, recognised by Buchner as leucocytic stimuli. I regard leucocytosis therefore, in agreement with Kurloff, as a function of the bone-marrow."
Of great theoretical interest is the contrast between eosinophil and neutrophil cells. At the height of ordinary leucocytosis, the number of eosinophil cells is diminished often to disappearance; whilst during its decline they occur in abnormally high numbers. Hence it follows that the eosinophil and neutrophil cells must react towards stimulating substances completely differently, and in a certain sense oppositely[27].
It seems, generally speaking, that the bacterial metabolic products formed in human diseases which are positively chemiotactic for the polynuclear neutrophil cells are negatively chemiotactic for the eosinophils, and vice versâ.