DEVELOPMENT OF BLOOD; S3 



division. In whichever way produced, however, whether from 

 the original formative cells of the embryo, or by the liver, these 

 colored nucleated cells begin very early in foetal life to be 

 mingled with colored non-nucleated corpuscles resembling those 

 of the adult, and about the fourth or fifth month of embry- 

 onic existence are completely replaced by them. 



The manner of origin of these perfect non-nucleated cor- 

 puscles 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 fcetal existence. 



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

 red corpuscles are derived from the smaller of the nucleated 

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



II. Concerning the Manner of their Development. 



There is not perfect agreement among physiologists concern- 

 ing the process by which lymph-globules or white corpuscles 

 (and in the foetus, perhaps the red nucleated cells) are trans- 

 formed 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 contents, 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. 



Of these two theories, that which supposes the nucleus of the 

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

 corpuscle is the theory now generally adopted. 



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. 



Without doubt, these little bodies 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, and we can only surmise that in these things 



