DEVELOPMENT OF BLOOD. 93 



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. 



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 they resemble more or less 

 closely those parts of the body which lie more plainly 

 within our observation. 



From what has been said, it will have appeared that when 

 the blood is once formed, its growth and maintenance are 

 effected by the constant repetition of the development of 

 new portions. In the same proportion that the blood yields 

 its materials for the maintenance and repair of the several 

 solid tissues, and for secretions, so are new materials sup- 

 plied to it in the lymph and chyle, and by development 

 made like it. The part of the process which relates to the 

 formation of new corpuscles has been described, but it is 

 probably only a small portion of the whole process ; for the 

 assimilation of the new materials to the blood must be 



