424 



THE BLOOD. 



[CH. xxvi. 



those of the adult, and at about the fourth or fifth month of 

 embryonic existence are completely replaced by them. 



Origin of the Matured Coloured Corpuscles. The non- 

 nucleated red corpuscles may possibly be derived from the nucle- 

 ated, but in all probability are an entirely new formation. Their 

 chief origin is : 



From the medulla of bone. It has been shown that coloured 

 corpuscles are to a very large extent derived during adult life 

 from the large pale cells in the red marrow of bones, especially of 

 the ribs. These cells become coloured from the formation of 

 haemoglobin chiefly in one part of their protoplasm. This coloured 

 part becomes separated from the rest of the cell and forms a red 

 corpuscle, being at first cup-shaped, but soon taking on the normal 

 appearance of the mature corpuscle. Mingled with the amoeboid 

 colourless marrow cells (p. 59) are a number of other smaller 



Fig. 356. Development of red corpuscles in connective tissue cells. From the subcutaneous 

 tissue of a new-born rat. h, a cell containing haemoglobin in a diffused form in the 

 protoplasm ; h', one containing coloured globules of varying size and vacuoles ; A", a 

 cell filled with coloured globules of nearly uniform size; /,/', developing fat cells. 

 (E. A. Schafer.) 



amoeboid cells called erythroblasts (fig. 358) ; these are tinted with 

 hfemoglobin ; they divide and multiply, lose their nucleus, and 

 are thus transformed into discoid blood-corpuscles. 



From the tissue of the spleen. It is probable that coloured as 

 well as colourless corpuscles may be produced in the spleen from 

 cells similar to the erythroblasts of red marrow. 



The belief which formerly prevailed that the red corpuscles are- 

 derived from the white or from the platelets has now been discarded. 



During foetal life and possibly in some animals, e.g. the rat, 

 which are born in an immature condition, for some little time 

 after birth, the blood discs have been stated by Schafer to arise in 

 the connective tissue cells in the following Avay. Small globules, 

 of varying size, of colouring matter arise in the protoplasm of 

 the cells (fig. 356), and the cells themselves become branched,, 

 their branches joining the branches of similar cells. The cells 

 next become vacuolated, and the red globules are free in a cavity 



