840 
PROFESSOR POUCHET. 
abundance in the blood in certain diseases by MM. Vanlair 
and Masius, and which they called microcytes. 
These old hsematids have the same general characters as 
those of oviparous animals. They lose in great part their 
elasticity, and seem to have on account of this a great ten- 
dency to be caught, and remain in the reticulum of the 
spleen where the blood coming from the arterial extremities 
falls into this spongy network, out of which open the large 
venous trunks. There is nothing to support the theory that an 
active destruction of blood-corpuscles goes on in any special 
organ. 
Origin of Blood in Mammals . — In mammals, as well as in 
birds, the first corpuscles are formed in the vascular area. 
I have been able to follow this formation in the rabbit, 
and to prove that haematids continue to be formed from the 
old walls of the umbilical vesicle, even when the embryo is 
as much as ram. long. 
If the chorion be removed from the surface of the egg 
the vascular area is exposed, this consists of a layer of 
similar cells. I have assured myself that the primitive or 
blastodermic cells differentiate in two ways, forming on the 
one hand the endothelial cells of the vascular walls, and 
on the other, the embryonic red corpuscles. The former 
envelop the latter, which latter, grouped in caeca opening 
on to the spaces already traversed by the blood, undergo a 
more or less complete development before being in their turn 
taken into the current. 
Here then the formation of the first red corpuscles is 
certainly not endogenous. 
The blastodermic cells destined to become red corpuscles 
ordinarily multiply to a greater or less extent by fission 
before undergoing haemoglobic degeneration. The older 
the embryo grows, the more this segmentation appears to 
give place to cells of smaller diameter, and the more rapidly 
does this degeneration of the cells proceed. 
At first the cells which go to form the haematids are very 
large, they pass into the circulating stream before the 
nucleus has disappeared, or at least before it has ceased to 
present the ordinary chemical characters of unclear sub- 
stance, these cells become the large embryonic haematids. 
Later on segmentation goes on more rapidly, and the result- 
ing cells are even smaller and the nucleus rapidly atrophies. 
This may go on in two ways, either the nucleus gradually 
diminishing in volume loses its chemical characters, takes 
on those of the protoplasm surrounding it (the final process 
in the haematids of oviparous animals, as I described above). 
