3. =The microblasts.= These are occasionally present, _e.g._ in traumatic anæmias, but they are very seldom found, and have not so far attracted particular attention.
The question of the meaning of the =normoblasts= and =megaloblasts= has led to lively and significant discussions, partly in favour of, partly against the distinction between these two cell forms. After surveying the literature, we are forced to separate the megaloblasts from the normoblasts, in the first place because of their subsequent histories, and the peculiarities of their nuclei, and secondly because of clinical observation.
[alpha]. =The fate of the nuclei.= For some time past two views, almost diametrically opposed, have been in existence with regard to the nature of the change of the nucleated to the non-nucleated erythrocytes. The chief exponent of the one, Rindfleisch, taught that the nucleus of the erythroblasts leaves the cell, which thereby becomes a complete erythrocyte, whilst the nucleus itself, by the aid of the small remnant of protoplasm which surrounds it, takes up new material from the surrounding plasma, manufactures hæmoglobin and so becomes a fresh erythroblast. According to the second theory the erythroblasts change to non-nucleated discs by the destruction and solution of the nucleus within the cell body. ("Karyorrhexis," "Karyolysis.") The authors who support this view and also describe it as the only kind of erythrocyte formation are chiefly Kölliker and E. Neumann.
Rindfleisch arrived at his theory by direct observation of the process described, as it occurred in physiological saline solution with the blood of foetal guinea-pigs and teased preparations of bone-marrow.
E. Neumann regards Rindfleisch's doctrine as untenable, since the process which he observed is chiefly the result of a severe injury of the blood from the sodium chloride solution and the teasing. If a method of preparation be chosen which protects the blood as far as possible, and avoids every chemical and physical alteration, the exit of the nucleus as described by Rindfleisch does not occur.
The view of Kölliker and Neumann that the nuclei gradually decay in the interior of the cell is not supported by the observation of a process, but by the fact that in suitable material, for instance, foetal bone-marrow, liver blood, and leukæmic blood, the transition from erythroblast to erythrocyte is shewn by all phases of nuclear metamorphosis. v. Recklinghausen professes to have directly observed the dissolution of the nucleus within the cell in rabbit's blood, kept living in a moist chamber. Pappenheim's opinion however, that in this case processes are concerned such as Maragliano and Castellino have described as artificial necrobiosis, seems in this connection worthy of consideration.