CHAPTER X

DISCOVERIES BY A GREEK AND BY AN ENGLISHMAN

Galen, the Greek, was born in the year 30 A.D. He made discoveries about the body, practiced medicine in Rome, and for fourteen hundred years afterwards what he had believed and written about the body of man was taught in every school of medicine in Europe.

This domination continued until William Harvey, an Englishman, made his discoveries. In 1616 we find him lecturing in London. He was thirty-eight years old at the time. When he died, at the age of seventy-nine, he had added such a volume of scientific facts to those which Galen had discovered, that during the three hundred years since then the two names have stood side by side on the honored roll of those who have transformed the beliefs of the human race.

Naturally, of course, Harvey began his work where Galen and his successors left off. He built on foundations which Galen had laid, but he was as independent of past beliefs as Galen himself had been. Whenever he had the opportunity, whether with men or animals, whether with those that were well or ill,

alive or dead, he studied their bodies and gave special attention to the action of the heart and to any connection which it might have with the blood supply.

In the case of wounded animals, at different times he laid his hand on the heart and noticed that with each throb the blood left the wound with a spurt, and he saw that blood which spurted in jets from a wound was always of the bright red kind.

Then too he came across wounds that bled in a different way. With them the blood simply poured out in a quiet, dark-purplish stream. In such cases there was no sudden increase of flow with the heart beat. He found that the same was true for wounds in man and beast alike; that is, bright blood came in jets while dark blood came in a quiet stream. Moreover, he saw that it was always true that when the heart beat slowly the pulse at the wrist was slow too.

These important observations, added to many experiments which he himself made, drew Harvey's thoughts more and more to questions about circulation. It then occurred to him that the heart might be a special machine for pumping bright-colored blood out into the arteries, and the thought of such a possibility was exciting even to himself.

Through yet other experiments and constant thought on the subject, his suspicions gradually changed to convictions. He became very sure that every pulse beat in

the artery at the wrist means that the heart has pumped a fresh supply of blood into the large artery, the aorta, which is joined directly to it, and that the elastic tubes have expanded throughout their entire length to make room for it. He knew, as we do, that the largest arteries are buried deeper in the body than the veins, and that only at certain spots do they come near enough to the surface to allow us to feel the effect of the heart beat. He noticed that there is never any throb in a vein, and this strengthened his conviction that no vein ever receives blood directly from the throbbing heart.

By traveling the road which he took we have come upon Harvey's first great discovery:

The heart pumps blood into the arteries.

The scientific world was even more excited over this announcement than it had been over Galen's discovery. But Harvey himself went quietly on with his investigations. He saw that the heart pumps by contracting and expanding; that the average human body holds about six quarts of blood; that the heart sends about half a tumblerful of blood into the aorta every time it contracts; and that, since the heart beats about seventy times a minute, an enormous quantity of blood must be squeezed out of it during each half hour.

He did some multiplying, as we ourselves might do just here, and decided that if the heart sends out over

one thousand tumblerfuls of blood every hour, and if the body holds no more than twenty-four tumblerfuls, — that is, six quarts, - the enormous supply must be explained somehow. Where did it all come from? This was Harvey's next great problem.

One sign after another led him to suspect that the veins might hold the explanation. He therefore tested veins and arteries too,

as we ourselves may do. Draw up your sleeve, swing your arm round your head once or twice,

A

B

POCKET VALVES IN THE VEINS

4 shows a vein slit lengthwise and laid open; B shows a vein cut through lengthwise; C shows how a vein looks from the outside

when its valves are filled with blood

let it hang by your side for a minute, and you will notice that some of the blood vessels appear as dark lines under the skin. Stroke these lines down towards the wrist. They are veins, and the little bunches which stand out show where the valves have caught the blood. Remember that these valves are on the inside lining of every vein, and that they always open towards the heart. During the time, then, that the blood in the veins flows steadily towards the heart, the valves lie flat and smooth against the lining and you would not suspect their presence. But try to drive that blood away from the heart, and quickly every valve is so

filled that it stands out like a little pouch and helps block the passage of the blood backwards. The nature of the veins, therefore, helped Harvey on towards his next discovery.

While your left arm is still uncovered, press and squeeze it with your right hand, stroking towards the

elbow to hasten the blood out of

the veins. Now, as quickly as you

A HANDKERCHIEF AND A STICK
TO COMPRESS AN ARTERY
As the stick is turned the band-
age is pulled tighter

Arteries are buried deep, veins are near the surface. Your bandage is therefore checking the flow in both sets of blood vessels; and because no blood can get into the arm, the color of it stays about as when you tied the bandage. Above the elbow, however, you feel a throbbing, because the blood in the arteries is held back by the dam of the bandage. Loosen this bandage a little. You have now lifted the pressure from the arteries, and blood hurries

(After Tracy)