THE BLOOD. 169 



are traces of nuclear material in the non-nucleated corpuscles. Owing 

 to these facts and other recent investigations, Maximow asserts that 

 while the greater part of the nucleus is extruded, still a small portion 

 usually remains in a finely granular form and gives a basic staining 

 quality to the centres, especially of the young red cells. 



Origin of the Mature Colored Corpuscles. It has already 

 been shown that during uterine life the marrow gradually assumes more 

 and more completely the function of forming red cells. This function 

 prevails after birth, and most authorities now regard the red marrow as 

 the exclusive seat, under normal conditions, of the production of red 

 corpuscles. The original cell, or erythroblast, is generally considered to 

 be a large colorless cell which is devoid of hemoglobin, is larger than 

 the ordinary red cell, and has a single nucleus but no nucleolus; it 

 differs but very slightly from the original mesoblastic cell. 



By mitotic division of these original cells there are derived several 

 series of cells which approach, more and more completely, the type of 

 nucleated red corpuscles, becoming rich in haemoglobin. The nucleus 



* 



Fig. 144. Colored nucleated corpuscles, from the red marrow of the guinea-pig. (E. A. Schafer. ) 



is then extruded (or partly extruded and partly broken up) and the 

 normal non-nucleated red corpuscle results. A few authorities, how- 

 ever, in tracing the red cells back to colorless cells, think that all the 

 lymphoid tissues are also probable sources of the erythroblasts. In in- 

 fancy and early childhood the red marrow, which produces the colored 

 corpuscles, is found in large amount in the cavities of almost all the 

 bones. In adult life it is normally confined to the ribs, flat bones, 

 vertebrae, and upper and lower thirds of the long bones. In pathological 

 conditions it has been found that the spleen in the adult, or both the 

 spleen and the liver in infancy and early childhood, can resume the 

 function of producing red corpuscles. 



Without doubt, the red corpuscles have, like all other parts of the 

 organism, a tolerably definite term of existence, and in a like manner 

 die and waste away when the portion of work allotted to them has been 

 performed. Neither the length of their life, however, nor the fashion 

 of their decay has been yet clearly made out. It is generally believed 

 that a certain number of the colored corpuscles undergo disintegration 

 in the spleen ; and indeed corpuscles in various degrees of degeneration 

 have been observed in that organ. 



Origin of the Colorless Corpuscles. In foetal life the white 

 corpuscles are not found in the blood until the vascular system has been 



