TRANSACTIONS OF THE SECTIONS. 153 
lar pressure upon the brain. It was also ascertained, that though the 
pulse begins to diminish much in frequency about the time that the 
insensibility occurs, yet that this has not taken place to such an extent 
at the precise time when the insensibility has supervened, as to lead us 
to believe that it depends upon any diminished transmission of blood 
through the vessels of the brain. From these facts it is concluded, that 
the insensibility principally, if not entirely, depends upon the circulation 
of venous blood in the vessels of the brain. It was remarked, that the 
blood in the exposed arteries was of a decidedly dark hue before the 
struggles preceding the insensibility occurred, and thus showed the in- 
conclusiveness of those experiments in which unsuccessful attempts 
were made to induce coma by injecting venous blood slowly into one 
_ of the four arteries leading to the brain. In performing experiments 
upon this subject, it is necessary to bear in mind the exact period at 
which the insensibility presents itself. A dog generally becomes in- 
sensible in about two minutes, to two minutes and a half, and a rabbit 
generally in about one minute and a half, after the complete exclusion 
- of air from the lungs; so that any experiment made upon the quantity 
of blood which flows from the cut arteries at periods posterior to this, 
cannot with safety be adduced in explanation of effects which have 
previously happened. 
On the Anatomical relation of the Blood-vessels of the Mother to those 
of the Fetus in the Human Species. By Dr. Joun Rerp. 
In this communication it was proved, by preparations laid on the 
table, that numerous tufts of the placental vessels pass through the 
decidua and enter by the open mouths of many of the uterine venous 
sinuses of the mother. Some of these tufts only dip into the open 
mouths of the sinuses, while others extend their ramification half an 
inch, and even in some rarer cases more than an inch from the point at 
which they enter. That these tufts found bathed in the maternal blood 
of the uterine venous sinuses are prolongations of the fcetal placental 
vessels, was proved both by injection and by microscopic examination. 
Dr. Reid then proceeded to point out that each minute placental artery 
was bound up with a placental vein, and that they terminated in blunt 
extremities, where these two sets of vessels communicated. The in- 
tervals left between the branches of the tufts of the placenta are not 
filled up with cellular tissue, but the surface of every branch of a tuft 
is covered by a prolongation of the inner coat of the vascular system 
of the mother, or at least by a thin membrane continuous with it. 
This membrane constitutes a kind of sac, with numerous and intricate 
folds or fringes projecting into its interior. These folds are formed by 
the covering which it affords to the numerous branches of the placental 
vessels. Into this sac the blood of the mother is poured by the curling 
arteries, and is returned by the prolongations of the uterine veins. 
Each of the uterine sinuses into which the placental tufts project, may 
be considered a miniature representation of the structure of the placenta; 
