in free and tie and compress the arteries at some
distance from the heart, you will see, on the contrary, their included
portion grow excessively turgid, the heart becoming so beyond measure,
assuming a dark-red color, even to lividity, and at length so overloaded
with blood as to seem in danger of suffocation; but when the obstruction
is removed it returns to its normal condition, in size, color, and
movement."(4)

This conclusive demonstration that the veins return the blood to the
heart must have been most impressive to Harvey, who had been taught to
believe that the blood current in the veins pursued an opposite course,
and must have tended to shake his faith in all existing doctrines of the
day.

His next step was the natural one of demonstrating that the blood passes
from the arteries to the veins. He demonstrated conclusively that this
did occur, but for once his rejection of the ancient writers and one
modern one was a mistake. For Galen had taught, and had attempted
to demonstrate, that there are sets of minute vessels connecting the
arteries and the veins; and Servetus had shown that there must be such
vessels, at least in the lungs.

However, the little flaw in the otherwise complete demonstration of
Harvey detracts nothing from the main issue at stake. It was for others
who followed to show just how these small vessels acted in effecting
the transfer of the blood from artery to vein, and the grand general
statement that such a transfer does take place was, after all, the
all-important one, and the exact method of how it takes place a detail.
Harvey's experiments to demonstrate that the blood passes from the
arteries to the veins are so simply and concisely stated that they may
best be given in his own words.

"I have here to cite certain experiments," he wrote, "from which it
seems obvious that the blood enters a limb by the arteries, and returns
from it by the veins; that the arteries are the vessels carrying the
blood from the heart, and the veins the returning channels of the blood
to the heart; that in the limbs and extreme parts of the body the
blood passes either by anastomosis from the arteries into the veins, or
immediately by the pores of the flesh, or in both ways, as has already
been said in speaking of the passage of the blood through the lungs;
whence it appears manifest that in the circuit the blood moves from
thence hither, and hence thither; from the centre to the extremities, to
wit, an