William Harvey

by Sir D'Arcy Power

The broad points in connection with the vascular system being thus settled, Harvey turned his attention more particularly to the mechanism of the heart’s action. He shows that the two auricles move synchronously and that the two ventricles also contract at the same time. Hitherto it had been supposed that each cavity of the heart moved independently, so that every cardiac cycle consisted of four distinct movements. To prove that the movement of the heart was double he examined the eel, several fish, and some of the higher animals. He noticed that the ventricles would pulsate without the auricles, and that if the heart were cut into several pieces “the several parts may still be seen contracting and relaxing.” The minute accuracy of Harvey’s observation is shown by his record of what is in reality a perfusion experiment. He says: “Experimenting with a pigeon upon one occasion after the heart had wholly ceased to pulsate and the auricles too had become motionless, I kept my finger wetted with saliva and warm for a short time upon the heart and noticed that under the influence of this fomentation it recovered new strength and life, so that both ventricles and auricles pulsated, contracting and relaxing alternately, recalled as it were from death to life.” We now know that this was due to the warmth, to the moisture, and to the alkalinity of Harvey’s saliva, so that he performed crudely, and no doubt by accident, one of the most modern experiments to show that the heart, under suitable conditions, has the power of recovering from fatigue.

This portion of the treatise affords an insight into the enormous amount of labour which Harvey had expended in its production, for he says: “I have also observed that nearly all animals have truly a heart, not the larger creatures only and those that have red blood, but the smaller and pale-blooded ones also, such as slugs, snails, scallops, shrimps, crabs, crayfish, and many others; nay, even in wasps, hornets, and flies I have, with the aid of a magnifying glass and at the upper part of what is called the tail, both seen the heart pulsating and shown it to many others.” That this was the result of a careful study of the animals mentioned and not a simple observation is shown by the following sentences: “In winter and the colder season, pale-blooded animals such as the snail show no pulsations: they seem rather to live after the manner of vegetables or of those other productions which are therefore designated plant animals.... We have a small shrimp in these countries, which is taken in the Thames and in the sea, the whole of whose body is transparent: this creature, placed in a little water, has frequently afforded myself and particular friends an opportunity of observing the movements of the heart with the greatest distinctness, the external parts of the body presenting no obstacle to our view, but the heart being perceived as though it had been seen through a window.

“I have also observed the first rudiments of the chick in the course of the fourth or fifth day of the incubation, in the guise of a little cloud, the shell having been removed and the egg immersed in clear, tepid water. In the midst of the cloudlet in question there was a bloody point so small that it disappeared during the contraction and escaped the sight, but in the relaxation it reappeared again red and like the point of a pin.”

Harvey formulates in his fifth chapter the conclusions to which he had been led about the movement, action, and use of the heart. His results appear to be absolutely correct by the light of our present knowledge, and they show how much can be done by a careful observer, even though he be unassisted by any instrument of precision.

“First of all the auricle contracts, and in the course of its contraction forces the blood (which it contains in ample quantity as the head of the veins, the storehouse and cistern of the blood) into the ventricle which, being filled, the heart raises itself straightway, makes all its fibres tense, contracts the ventricles and performs a beat, by which beat it immediately sends the blood supplied to it by the auricle into the arteries. The right ventricle sends its charge into the lungs by the vessel which is called the vena arteriosa [pulmonary artery], but which in structure and function and all other respects is an artery. The left ventricle sends its charge into the aorta and through this by the arteries to the body at large.

“These two movements, one of the ventricles, the other of the auricles, take place consecutively, but in such a manner that there is a kind of harmony or rhythm preserved between them, the two concurring in such wise that but one movement is apparent, especially in the warmer blooded animals in which the movements in question are rapid. Nor is this for any other reason than it is in a piece of machinery in which, though one wheel gives movement to another, yet all the wheels seem to move simultaneously; or in that mechanical contrivance which is adapted to firearms, where the trigger being touched, down comes the flint, strikes against the wheel, produces a spark, which falling among the powder, ignites it, upon which the flame extends, enters the barrel, causes the explosion, propels the ball, and the mark is attained—all of which incidents by reason of the celerity with which they happen, seem to take place in the twinkling of an eye.... Even so does it come to pass with the movements and action of the heart.... Whether or not the heart besides propelling the blood, giving it movement locally and distributing it to the body, adds anything else to it—heat, spirit, perfection—must be inquired into by and by, and decided upon other grounds. So much may suffice at this time, when it is shown that by the action of the heart the blood is transfused through the ventricles from the veins to the arteries and is distributed by them to all parts of the body.

“The above indeed is admitted by all, both from the structure of the heart and the arrangement and action of its valves. But still they are like persons, purblind or groping in the dark, for they give utterance to various contradictory and incoherent sentiments, delivering many things upon conjecture.... The great cause of doubt and error in this subject appears to me to have been the intimate connection between the heart and the lungs. When men saw both the pulmonary artery and the pulmonary veins losing themselves in the lungs, of course it became a puzzle to them to know how or by what means the right ventricle should distribute the blood to the body or the left draw it from the venae cavae....

“Since the intimate connection of the heart with the lungs, which is apparent in the human subject, has been the probable cause of the errors that have been committed on this point, they plainly do amiss who, pretending to speak of the parts of animals generally, as Anatomists for the most part do, confine their researches to the human body alone, and that when it is dead. They obviously do not act otherwise than he who, having studied the forms of a single commonwealth, should set about the composition of a general system of polity: or who, having taken cognisance of the nature of a single field, should imagine that he had mastered the science of agriculture; or who, upon the ground of one particular proposition, should proceed to draw general conclusions.

“Had Anatomists only been as conversant with the dissection of the lower animals as they are with that of the human body, the matters that have hitherto kept them in a perplexity of doubt would, in my opinion, have met them freed from every kind of difficulty.”

After this plea for the employment of comparative anatomy to elucidate human anatomy, Harvey proceeds to deal in a most logical manner with the various difficulties in following the course taken by the blood in passing from the vena cava to the arteries, or from the right to the left side of the heart. He begins with fish, in which the heart consists of a single ventricle, for there are no lungs. He then discusses the relationship of the parts in the embryo, and arrives at the conclusion that “in embryos, whilst the lungs are in a state of inaction, performing no function, subject to no movement any more than if they had not been present, Nature uses the two ventricles of the heart as if they formed but one for the transmission of the blood.” He therefore concludes that the condition of the embryos of those animals which have lungs, whilst these organs are yet in abeyance or not employed, is the same as that of the animals which have no lungs. From this he wishes it to be understood that the blood passes by obvious and open passages from the vena cava into the aorta through the cavities of the ventricles. A statement which was in direct opposition to the generally received tradition of the time that the blood passed from the right into the left ventricle by concealed pores in the septum which separates the two cavities in the heart.