220 MORPHOLOGY OF THE RED CORPUSCLES. 



appear to be undergoing division (fig. 257). They are amoeboid cells, the protoplasm 

 of which is coloured by haemoglobin, and they closely resemble, in fact, the nucleated 

 red blood-corpuscles of the embryo. It appears therefore probable that the cells 

 in question are descendants of the embryonic red blood -corpuscles, and that they 

 are transformed into the ordinary blood-discs by the gradual atrophy and disappear- 

 ance of the nucleus and the moulding of the coloured cell-substance into the shape 

 of the biconcave red corpuscles. Appearances such as are exhibited by some of the 

 corpuscles which are delineated in fig. 257, certainly indicate atrophy of the 

 nucleus. 1 The amoeboid movements of which these corpuscles are capable may assist 

 them to pass into the blood-capillaries, the walls of which are, in mammals, less 

 distinct and continuous than in other parts, with the single exception of the spleen. 

 But it would appear from the observations of Bizzozero and Torre that in birds the 

 capillary walls are complete, and that all the erythroblasts are intravascular, i.e., are 

 found within the venous capillaries and not in the tissue of the marrow. These 

 venous capillaries are relatively large, and the blood-stream in them must be 

 exceedingly slow. The fully developed red corpuscles lie in the axis of the vessel, 

 the erythroblasts and leucocytes towards the periphery. 



These statements have been confirmed in the main by Denys, who has also subjected the 

 marrow in birds to a careful examination. Denys states, however, that the coloured erythro- 

 blasts are derived from colourless erythroblasts lying next to the capillary wall, and that 

 while this transformation into red corpuscles is going on within the vessels, the marrow cells 

 outside the vessels are multiplying and forming white blood corpuscles. 



3. Origin from white corpuscles. The view which long obtained most prevalence, is 

 that the red discs are developed from the white corpuscles. There are, however, no recorded 

 observations of recent date which show conclusively that the red corpuscles are thus developed 

 in the circulating blood, although some observers are of opinion that such transformation may 

 occur in the marrow. 



4. In the spleen. It has long been believed that the formation of red blood-corpuscles is 

 carried on in the spleen-pulp, but this view has been in many quarters supplanted by the con- 

 trary one that a destruction of red corpuscles rather than a new formation may there take 

 place, in support of which many facts were brought forward by Kolliker. The former view 

 has, however, been again brought into prominence by Bizzozero, who describes in the spleen- 

 pulp after severe loss of blood, nucleated red corpuscles like those in the marrow, and further 

 finds that there are more red as well as white corpuscles in the blood of the splenic vein than 

 in that of the corresponding artery. These statements only apply, however, to certain animals. 



5. From the elementary particles or blood-platelets. Hayem described these as the 

 precursors of the red blood-corpuscles in mammals. To them he applied the name 

 " hsematoblasts," and he maintains that they acquire colour, and by a gradual increase in size 

 become directly transformed into red corpuscles. In support of this view he points out that 

 red corpuscles which are much smaller than the ordinary ones are to be almost always met 

 with in blood, and that these smaller forms are especially numerous in cases where there 

 has been previously a considerable loss of blood, and in which, therefore, it may well be sup- 

 posed that a new formation of red corpuscles is proceeding ; and further, that they present 

 every transition between the blood-tablets and the red discs. 2 In the frog Hayem 

 describes as hjematoblasts, spindle-shaped cells something like the white corpuscles, but of 

 more delicate appearance (like the corpuscle marked j> in fig- 245). These become, according 

 to him, converted directly into red corpuscles, after undergoing an increase of size and a 

 change of shape, in addition to the accession of colouring matter. They had been long 

 previously noticed by Recklinghausen, and regarded as transition forms between the white 

 and red corpuscles. 



Morphology of the red corpuscles. It is obvious from the study of the 

 structure of the mammalian red blood-disks that they are not morphologically to 

 be regarded as cells. For they lack a most important morphological constituent of 

 the cell, viz., the nucleus, nor do they exhibit any other sign of cell-structure. 



1 According to Howell the partially atrophied nucleus becomes extruded, and then dissolved. 



2 A similar account of the development of the red discs was given by Zimmermann ; but many of 

 the transitional forms which he described were red corpuscles which had become decolorised. The 

 same may probably be said regarding the "invisible corpuscles " of Norris (" Physiology and Pathology 

 of the Blood," 1882). 



