58 Transadions of the 



imparts to the embryo-corpuscles within them a granular aspect, 

 but without discolouring them. The older fully- developed blood 

 corpuscles undergo also a discolouration by the action of this solu- 

 tion, in consequence of which they are seen in the interior of the 

 smaller blood-vessels in the form of clear, double-contoured cells. 

 The younger ones remain, with the exception of an inconsiderable 

 diminution of their diameter, unchanged — that is, they retain their 

 colouring matter, which assumes, by the action of the chromic acid, 

 a greenish shining appearance ; these are but seldom met with in 

 the finer capillaries. It must here be mentioned, that the mother- 

 blood corpuscles, in general, are naturally somewhat paler than the 

 embryo-corpuscles which they contain, and that the loss of colour 

 is not always due to the action of the chromic acid solution ; on 

 the contrar}^, I have sometimes observed clear double-contoured 

 mother-bodies in fresh blood. Small blood crystals are sometimes 

 seen in the interior of the smaller blood-vessels or in the embryonic 

 blood corpuscles themselves, especially in such specimens as have 

 remained for some time in a chromic acid solution. On the ma- 

 tured blood corpuscles of tliis period, the same changes of form are 

 observed as occur in those of the adult. More especially are they 

 inclined to assume a cup-shaped form by the swelling of their 

 margins, and this takes place sometimes to such a degree that they 

 assume the form of a hollow sphere, on which nothing more than 

 a small orifice remains, bounded by the contracted margin. In 

 regard to the colourless blood corpuscles, it may here be mentioned, 

 that up to this period none of them were observed either in the 

 heart or in the blood-vessels. 



The further now the embryo advances in its development, and 

 the more that blood-forming organ, the spleen, attains to pei^^ection, 

 the rarer becomes the primary endogenous formation of the coloured 

 blood corpuscles ; nevertheless a considerable number of mother- 

 corpuscles, as we shall see directly, are still met with at the begin- 

 ning of the fourth month. The greater portion of the fresh blood, 

 taken from the heart of an embryo about twelve weeks old, con- 

 sisted accordingly of fully-developed corpuscles, that is, such as 

 were marked by a round margin and a central concavity (Fig. 6, a) ; 

 their diameter differed considerably, and ranged from ^§0 to :i^o mm. 

 In addition to these, I observed still a number of mother-blood cor- 

 puscles, the most of which contained but one embryo- corpuscle 

 (Fig. 6, h). The size of the latter, however, did not stand in due 

 proportion to their maturity, as a number of them had already 

 attained a diameter of^o mm., while, on the other hand, a number 

 of young, already liberated corpuscles (Fig. 6, c), had scarcely 

 attained one of -^^ mm. 



In the same blood I also met with some young blood corpuscles, 

 just in the act of detaching themselves from the mother-corpuscle; 



