100 MALL. [Vov. XIX. 
there is much mother’s blood and within them there is a well- 
developed system of capillaries filled with embryo’s blood. 
There are numerous leucocytes in the decidua, but they do 
not form abscesses. 
The front end of the amnion is wanting and its free ends 
are well imbedded in reticular magma, showing that this 
injury took place before the abortion was produced. The 
embryo is normal in form, the heart and blood-vessels well 
developed and filled with blood. The rest of the organs are 
about of the same stage at No. 391, an embryo of the four- 
teenth day. The tissues of the embryo and the ventricle of 
the fore-brain are filled with numerous small round cells with 
fragmented nuclei. Most of the blood corpuscles are still 
within the blood-vessels, but those within the tissues are per- 
fectly normal and in no way do they seem to give rise to the 
strange cells in the tissues. However, it may be noted that 
the mesodermal cells are diminished in number in those tis- 
sues in which the round cells are present, which indicates that 
the one changes into the other. The primary histological 
change in this embryo is found in the mesoderm, which is 
dissociating to form some of the so-called wandering cells. 
Later this process affects the wall of the vascular system and 
the blood cells escape into the tissues, as was pointed out by 
His. The cells within the ventricle of the brain as well as 
those of the neural tube are mostly fragmented and have be- 
tween them a few normal blood corpuscles. It is probable 
that most of these new cells arise from the dissociated nervous 
tissue. J shall come back to this question from time to time 
as I discuss specimens which have changes within them that 
bear upon this point. However, this much is clear: the round 
cells with fragmented nuclei lying within the tissues have not 
emigrated from the blood, but, instead, have arisen by a pro- 
cess of dissociation of the tissues within which they lie. 
The process of dissociation, begun in No. 250, is carried to 
an extreme degree in No. 321. Both of the embryos are of 
the same size, but in the second the amnion and chorion have 
continued to grow. The chorion is normal in appearance and 
