β. in anæmia etc. from defective action of the bone-marrow.
We have entered more fully into the leukopenia experimentally produced by Löwit, in the chapter on leucocytosis. We there explained, that according to present views, we have to deal, not with an actual destruction of the white elements, but merely with an altered distribution within the blood-stream.
Amongst the infectious diseases where an hypoleucocytosis occurs, typhoid fever must first be mentioned. The diminution is chiefly at the expense of the polynuclear cells. Uncomplicated measles too, generally runs its course with a marked leukopenia, specially distinct during the breaking out and at the height of the exanthem. These cases of infectious leukopenia are to be explained, not by a destruction of white corpuscles, but rather by a diminished inflow, brought about by the circulation of substances negatively chemiotactic for the polynuclear elements.
Leukopenia has still another meaning in certain cases of severe anæmia, where it indicates a highly unfavourable prognosis. Ehrlich has described (Charité Annalen 1888) a case of posthæmorrhagic anæmia ending fatally, where an extreme diminution of the leucocytes occurred. Exact figures shewed that the greater proportion (80%) of white blood corpuscles consisted of lymphocytes, whilst the polynuclears amounted to 14% (instead of 70-72% normally). Eosinophil cells and nucleated red blood corpuscles were entirely absent. Ehrlich explained these phenomena by a deficient activity of the bone-marrow, which found expression in the insufficient formation of red and white blood corpuscles. As the anatomical basis of this deficient activity, he conjectured that in this case the fatty marrow of the big long bones could not have been changed to blood forming red marrow, as is the rule in severe anæmias. In two cases the autopsy fully confirmed this diagnosis made during life.
The blood platelets.—The hæmoconiæ.
The blood-platelets were first described by Hayem, later by Bizzozero, as a third formed element of normal blood. They are roundish or oval discs free from hæmoglobin. They are extremely unstable under mechanical, thermal, and chemical influences. Their size amounts to some 3 µ. Specially characteristic is their tendency, the result of their extraordinary stickiness, to run together into largish clumps, "grape clusters." This circumstance greatly facilitates the distinction of the blood platelets from the other formed elements, but renders their enumeration most difficult. The apparatus usually used for counting the blood corpuscles is, for this reason, deceptive; for the platelets rapidly cling to its walls and remain there. All early authors (e.g. Bizzozero) endeavoured to obviate this error by some particular diluting fluid; but a number of these elements still remained fastened to the walls of the capillary tube of the mixing apparatus.
Recently Brodie and Russell have recommended a new mixture in which the platelets remain quite isolated, and are stained at the same time. They allow the drop of blood as it comes from the puncture to enter a drop of the fluid, and then estimate the relative proportion of red blood corpuscles to platelets[36]. The prescription for their solution is as follows:
Dahlia-glycerin,
2% solution of common salt ... equal parts.
Another method, used by the majority of more recent authors, is the relative enumeration of blood platelets in the stain dry specimen. Ehrlich found that the blood platelets were picked out by their deep red colour, corresponding to the amount of alkali they contain, in preparations treated by the iodine eosine method (see p. 46). Rabl's new method is much more complicated and in no way more serviceable, depending on a stain with iron hæmatoxylin recommended by E. Haidenhain for demonstration of the centrosomes. A process of Rosin's, not yet published, is more convenient. It consists in fixing the dry preparation for 20 minutes in osmic acid vapour, and staining in a concentrated watery solution of methylene blue.