CHAP. XXVII.] CHEMICAL ANALYSIS OF THE BLOOD. 307 



advanced periods of life. In mammalian embryos they are de- 

 scribed " as of large size, spherical or oval, pellucid and colourless, 

 nucleated and full of minute granules." Mr. Paget, whose 

 description we follow, confirms the observation made by Kolliker, 

 Fahrner, and others, of the occasional occurrence of " a process of 

 multiplication by bi-partition of the nucleus, each of which, either 

 by appropriating half the cell, or by developing a cell around itself, 

 becomes the central nucleus of a new cell differing from the parent 

 cell from which it escapes, in little except in being smaller and 

 more generally circular."* 



Of the manner in which the blood-corpuscles decay we really 

 know nothing no more than of the mode of decay of the elements 

 of the tissues. The notion held, for a time, by some physiolo- 

 gists, that the existing particles gave birth to new ones by a gem- 

 miparous or fissiparous generation, has no foundation in careful 

 observation. And it is most probable that, as Mr. Paget remarks, 

 " new corpuscles never appear to be produced from the germs of 

 old ones : when a corpuscle is past its perfection, it degenerates and 

 probably liquefies." "The changes of such degeneration," adds 

 this excellent observer, " have not been clearly seen in mamma- 

 lian corpuscles; but they are probably nearly similar to what 

 occur in those of fish and reptiles : in which the old and degenerate 

 corpuscles appear perfectly white and pellucid (not shaded or gra- 

 nular, like the lymph-corpuscles), smaller than they were, and in 

 some instances, cracked, or as if eroded. The nuclei appear to 

 degenerate with the cells, but, because of their darker and harder 

 outlines, remain longer distinct, and often look like free nuclei, 

 unless the dim cell-wall round them be carefully searched for. But 

 in this process, 110 germ for a new corpuscle issues from the 

 transient cell. Every new corpuscle forms itself in and from 

 the materials of the lymph and chyle, and is perfected in the 

 blood, and the blood is maintained by constant repetitions of this 

 process." f 



Kolliker has lately put forward the remarkable opinion, that the 

 spleen is the seat of a process of destruction or dissolution of the 

 blood-corpuscles. We shall examine this view farther on, when 

 we come to describe the structure of the spleen. J 



IV. The Chemical Analysis of the Blood. The blood is a fluid 

 of the greatest complexity, as must be expected if we regard it 

 as containing the material for the nutrition of all the tissues, as 



* Kirkea's Hand-Book of Physiology, p. 65, fig. 3. 



t Loc. cit. p. 70. J Art. Spleen, Cyclop. Anat. and Phys. 



