168 HANDBOOK OF PHYSIOLOGY. 



spleen. These are at first colorless and nucleated, but afterward ac- 

 quire the ordinary blood-tinge, and resemble very much those of the first 

 set. They also multiply by division. About this time the bone marrow 

 also begins to form red corpuscles, though at first in small amounts 

 only. This function develops rapidly, however, so that at birth the 

 marrow represents the chief seat of production of the red cells. Never- 

 theless, nucleated red cells are usually found at birth, sometimes in con- 

 siderable quantities, in the liver, and, less often, the spleen. Non- 

 nucleated red cells begin to appear soon after the first month of foetal 

 life, and gradually increase, so that at the fourth month they form one- 

 fourth of the whole amount of colored corpuscles; at the end of foetal life 

 they almost completely replace the nucleated cells. In late foetal life 

 the red cells are formed in almost the same way as in extra-uterine life. 



Various theories have prevailed as to the mode of origin of the non- 

 nucleated colored corpuscles. For a time it was thought that they were 

 of endoglobular origin, and merely fragments of some original cell, be- 

 ing produced by subdivision of the cell body itself. This theory easily 

 accounted for the absence of the nuclei, but it has not been supported 

 by recent investigations. At present it is the general belief that the 



Ct^ 





142. 143. 



i '*' W3 Multiplication of the nucleated red corpuscles. Marrow of young kitten after 

 bleeding, showing above karyokinetic division of erythroblast, and below the formation of 

 mature from immature erythrocysts. (Adapted from Howell ) 



1 2 * 4 -Shows the way -in .which the nucleus escapes from the nucleated red corpuscles. 

 represent different stages of the extrusion noticed upon the living corpuscles a 



f fakSd ? 6 ? ^H 1 n ? b H d ^ I*" adult Cat> bled f Ur """ : 6 ' specimen from the ci?'- 

 n? AH kitten forty days old bled twice: c, specimens from fcfie blood of a foetal cat, 

 S ^ "if- iarrow u of an adult cat, two of the figures showing the granules 

 efl ) aW 6n iDterpreted erroneously as?a sign of the"disint5gration 



non-nucleated cells are derived from nucleated cells by a process of mi- 

 totic division, and further that their nuclei gradually shrink or fade and 

 are then extruded. Extrusion undoubtedly occurs with great frequency, 

 but the use of some of the more recent stains seems to prove that there 



