(3) Nucleated red corpuscles, which occur in the blood of the foetus and the infant, gradually diminishing until at the third or fourth year they disappear. In the adult they do not occur in the blood in health, but are normal constituents of the red marrow of the short bones. They measure from 1/1500 to 1/2000 of an inch, and are of somewhat variable intensity of color, often quite as deep as the ordinary red forms. There may be two or even three nuclei, not colored, grouped together, often eccentric, and in some instances protruding from the cell.
(4) The hæmatoblasts of Hayem, the blood-plates of Bizzozero, the elementary or intermediate corpuscles, are small discoid colorless corpuscles about 3 µ in diameter, and are normal constituents of healthy blood. When the blood is withdrawn, they aggregate together into irregular clumps or masses, which have long been known as Schultze's granule-masses. It can be readily demonstrated in new-born rats or kittens, in which these masses abound, that the corpuscles composing them are isolated in the vessels, and only run together when the blood is drawn. The statement is commonly made that the granule-masses of Schultze result from the disintegration of the white corpuscle (of the red, Erhlich), but half an hour's study of the question in a new-born rat will convince any competent histologist that we have here to do with a separate blood-element.3 It appears to have important relations with the production of fibrin.
3 Consult Proceedings Royal Society, 1874; Centralblatt f. d. Med. Wissenschaften; Medical News, 1882, 2; Bizzozero, Virchow's Archiv, Bd. xi.; Hayem, Recherches sur l'Anatomie normal et pathologique du Sang, Paris, 1878.
Of the origin and life-history of the red corpuscles during post-embryonic life we have still much to learn. They are stated to develop—
(1) From colorless corpuscles, the lymph-cells or leucocytes. In the lymph-glands, the Malpighian bodies of the spleen, in the thymus, or the adenoid tissue of the tonsil, of the lymph-elements in the intestines and other regions, colorless cells are constantly being manufactured, and the general belief has been since Hewson's time that the red corpuscles develop in some way or other from these leucocytes. How or where has not yet been settled. It does not apparently go on in the blood, or we should surely catch, in the many observations and with the excellent powers now in use, a glimpse of the birth of one of them. Some observers (Johnstone4) maintain that they develop from the granular protoplasm of the adenoid reticulum by a process of budding. This may be so, but we should expect to find the lymph in the efferent vessels and of the thoracic duct much more rich in red cells than is usually the case, and in specimens of healthy glands we should find young-looking elements such as he describes.
4 Seguin's Archiv, vol. vi.
(2) From the nucleated red corpuscles. In the embryo this undoubtedly takes place, and as the weeks of development proceed, the ordinary red forms gradually predominate. In the child the red nucleated cells disappear early, and are then found only in the red marrow. So far as my observations go,5 they apparently originate from colorless marrow-cells, which gradually become more homogeneous, and hæmoglobin develops in the protoplasm. The nucleus degenerates and disappears, when the cell has the appearance of an ordinary red disk. Rindfleisch thinks that the nucleus of the nucleated red is extruded in the development. It is possible that from these nucleated red corpuscles cells may originate in another way—viz. by budding. This I have seen and sketched in the marrow-cells,6 and Malassez has studied the same process.7 The gemmæ are small, and sprout from the protoplasm, not the nuclei, and when they break off they resemble the microcytes which occur so abundantly in certain anæmic states. Bizzozero8 holds that these nucleated red corpuscles are independent elements which do not develop from the colorless marrow-cells. They multiply by fission, and develop into the ordinary red forms with the disappearance of the nuclei. Several recent investigations support this view.9
5 Centralblatt f. d. Med. Wissensch., 1878.
6 Trans. Am. Ass. Ad. Science, 1882.
7 Archives de Physiologie, 1882.