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MICROSCOPICAL INVESTIGATION. 359
ment by these observers of the importance of the vessels
above mentioned in the preparation of the blood.
A series of investigations on the vascular system, on
the blood, its composition, elaboration, movement, etc.,
was soon added to the discovery of the circulation of
the blood. A. BORELLI was the first to formulate
the thought that the vascular system resembles a hydraulic
apparatus, and he attempted to calculate the force with
which the blood flows through the vessels. It must be
confessed that he arrived at inaccurate results, for the
circumstances which have to be considered in this
investigation were then not sufficiently known. Thus, for
instance, his estimation of the resistance offered by the
continually narrowing arteries was unduly high.* WILLIAM
COLE hereupon drew attention to the fact that the sum of
the transverse sections of the vessels increases with their
distance from the heart, and that the vascular system may
be represented as a cone, the base of which is the periphery
of the body and the apex the heart.f BELLINI showed that
the blood flows with less velocity in proportion as the
vessels become more and more divided into branches.
STEPHEN HALES sought to determine the force of the
blood-pressure and the velocity of the blood-current by a
series of experiments, and introduced for this purpose a
glass tube into the divided artery of a living animal, so
that he might observe how high the blood was raised in it. J
MOLYNEUX and LEEUWENHOEK observed under the micro­
scope the velocity of the blood-current.§ The Irish doctor,
ALLEN MOULIN, made the first attempt to determine the
quantity of blood contained in the body. He opened the
hearts of animals by vivisection, and from the quantity of
blood which they contained, and from the velocity of the
* ALF. BORELLI : De motu animalium, Lugd. Bat., 1685, i, p. 94 et seq.
t WILL. COLE: De'secretione animali, Genev. 1696,0. 7, p. 26.
X STEPHEN HALES: Haemostatique ou la statique des animaux ; a French
transl., with notes by DE SAUVAGE, Geneva 1744, of "Statical Essays."
§ Philos.Transactions, London 1685, No. 177, p. 1236.