Qualitative changes in the protoplasm of the poikilocytes are not to be observed, even by staining; and one may therefore ascribe to them complete functional power, and regard their production as a purposeful reaction to the diminished number of corpuscles. For by the division of a larger blood corpuscle into a series of homologous smaller ones, the respiratory surface is considerably increased.
C. A third morphological variation which anæmic blood may shew in the more severe degrees of the disease, is the appearance of =nucleated red blood corpuscles=.
Though we do not wish to enter here upon the latest questions concerning the origin of the blood elements, we must shortly indicate the present state of our knowledge of the nucleated red corpuscles.
Since the fundamental work of Neumann and Bizzozero, the nucleated forms have been generally recognised as the young stages of the normal red blood corpuscles. Hayem's theory, on the contrary, obstinately asserts the origin of the erythrocytes from blood-platelets, and has, excepting by the originator and his pupils, been generally allowed to drop.
Ehrlich had in the year 1880 pointed out the clinical importance of the nucleated red blood corpuscles, in as much as he demonstrated that in the so-called secondary anæmias, and in leukæmia, nucleated corpuscles of the normal size, "normoblasts"; in pernicious anæmia excessively large elements, "megaloblasts," "gigantoblasts" are present. At the same time Ehrlich mentioned that the megaloblasts also play a prominent part in embryonic blood formation.
In 1883 Hayem likewise proposed a similar division of the nucleated red blood corpuscles into two,
(1) the "globules nuclées géantes" which he found exclusively in the embryonic state, (2) the "globules nuclées de taille moyennes" which he found invariably present in the later stages of embryonic life, and in adults. Further, W. H. Howell (1890) found in cats' embryoes two kinds of erythrocytes, (1) very large, equivalent to the blood cells of reptiles and amphibia ("ancestor corpuscles"), and (2) of the usual size of the blood corpuscles of mammalia. And similarly more recent authors, H. F. Müller, C. S. Engel, Pappenheim and others, have adhered to the division of hæmatoblasts into normo- and megaloblasts. And it is on the whole recognised, that, physiologically, normoblasts are always present in the bone-marrow of adults, as the precursors of the non-nucleated erythrocytes; that the megaloblasts, however, are never found there under normal circumstances, but only in embryonic stages, and in the first years of extra-uterine life.