DEVELOPMENT OF BLOOD. 103 



The manner of origin of these perfect non-nucleated 

 corpuscles must be now considered. 



I. Concerning the Cells from which they arise. 



a. Before Birth. It is uncertain whether they are 

 derived only from the cells of the lymph, which, at about 

 the period of their appearance, begins to be poured into 

 the blood; or whether they are derived also from the 

 nucleated red cells, which they replace, or also from similar 

 nucleated cells, which Kolliker thinks are produced by 

 the liver during the whole time of foetal existence. 



b. After Birth. It is generally agreed that after birth 

 the red corpuscles are derived from the smaller nucleated 

 lymph or chyle-corpuscles, the white corpuscles of the Hood. 



II. Concerning the Manner of their Development. 



There is not perfect agreement among physiologists 

 concerning the process by which lymph-globules or white 

 corpuscles (and in the foetus, perhaps the red nucleated 

 cells) are transformed into red non-nucleated blood-cells. 

 For while some maintain that the whole cell is changed 

 into a red one by the gradual clearing up of the con- 

 tents, including the nucleus, it is believed by Mr. Wharton 

 Jones and many others, that only the nucleus becomes the 

 red blood-cell, by escaping from its envelope and acquiring 

 the ordinary blood-tint. 



We are not in a position at present, perhaps, to say 

 certainly which of these two theories is the true one, but 

 the last-mentioned that which supposes the nucleus of 

 the lymph or chyle globule to be the germ of the future red 

 blood-cell, is the theory now almost universally adopted, 

 at least in this country. 



The development of red blood-cells from the corpuscles 

 of the lymph and chyle continues throughout life, and there 

 is no reason for supposing that after birth they have any 

 other origin. 



