518 
THE PHYSIOLOGY OF THE BLOOD. 
placentae, whence some of the foetal veins arise and take up 
the blood. An objection which I would urge to this, and I 
think a very potent one, is, if this were the case, why have we 
not more fatal hemorrhages after parturition? If hemorrhage 
does occur, the blood is of a dark venous character. 
Some have said on this point that nature, ever wise, prepares 
the vessels for the changes. In answer to this, I would ask, how 
is it that in cases of abortion we have scarcely any hemorrhage, 
even in very sudden cases, and where nature can scarcely have 
had time to accomplish this preparation? 
A third, and most likely theory, in my opinion, and which has 
many supporters, is, — the arteries of the mother deposit in the 
cellular structure of the placenta a fluid (this, like all others, may 
be viewed as a secretion), differing in its properties from blood, 
and which is taken up by some of the veins of the foetus. This 
becomes mixed with that portion of the foetal blood which is 
returning by other veins which take their origin from some 
of the minute terminating capillaries of the arteries, and then 
anastomosing form larger ones, and ramify over the membranes, 
but principally through the amnion, where their course is very 
tortuous. I am inclined to believe, that here the watery or more 
liquid parts are separated, constituting, in a great measure, the 
liquor amnii, by which the fluid is rendered more fit for the sup- 
port of the foetus. If some important function is not performed 
here, why are the vessels so tortuous ? I am well aware that the 
secretion of urine which is evidently going on in the foetus 
would rid the blood of its watery parts to a certain extent ; still the 
tortuosity of the vessels remains to be accounted for. 
Passing through the umbilical cord, just before it reaches the 
umbilicus, are two veins ; these unite, forming one trunk, which 
proceeds into the abdominal cavity of the foetus, in order to reach 
the liver, where the blood is again subjected to a purifying pro- 
cess. This is another circumstance, in my opinion, in favour of 
this theory; since, if arterial blood were received from the 
mother, what necessity was there for its passage through the 
liver ? Why not go directly into the posterior cava ? That the 
liver secretes bile, and a large quantity too, is proved by the 
inspissated masses of this principle, which are found in the 
intestines of the foetus. 
The Foetal Circulation. 
The umbilical arteries of the foetus arise from the internal 
iliacs, and take their course by the latapl parts of the bladder, 
through the umbilicus, forming a great part of the umbilical 
