Fathers of Biology

by Charles McRae

He recognizes that the flesh of the heart is somewhat different to that of the muscles of voluntary motion. Its fibres are described as being arranged in longitudinal and transverse bundles; the former by their contractions shortening the organ, the latter compressing and narrowing it. Such statements show that he regarded the heart as essentially muscular. He thought, however, that it was entirely destitute of nerves. Although he admitted that possibly it had one small branch derived from the nervus vagus sent to it, yet he entirely overlooked the great nervous plexus surrounding the roots of the blood-vessels, from which branches proceed in company with the branches of the coronary arteries and veins, and penetrate the muscular substance of the ventricles. He endeavoured to prove, by experiment, observation, and reasoning, that the arteries as well as the veins contained blood, and in this connection he tells an amusing story. A certain teacher of anatomy, who had declared that the aorta contained no blood, was earnestly desired by his pupils, who were ardent disciples of Galen, to exhibit the requisite demonstration, they themselves offering animals for the experiment. He, however, after various subterfuges, declined, until they promised to give him a suitable remuneration, which they raised by subscription among themselves to the amount of a thousand drachmæ (perhaps £30). The professor, being thus compelled to commence the experiment, totally failed in his attempt to cut down upon the aorta, to the no small amusement of his pupils, who, thereupon taking up the experiment themselves, made an opening into the thorax in the way in which they had been instructed by Galen, passed one ligature round the aorta at the part where it attaches itself to the spine, and another at its origin, and then, by opening the intervening portion of the artery, showed that blood was contained in it.

The arteries, Galen thought, possessed a pulsative and attractive power of their own, independently of the heart, the moment of their dilatation being the moment of their activity. They, in fact, drew their charge from the heart, as the heart by its diastole drew its charge from the vena cava and the pulmonary vein. The pulse of the arteries, he also thought, was propagated by their coats, not by the wave of blood thrown into them by the heart. He taught that at every systole of the arteries a certain portion of their contents was discharged at their extremities, namely, by the exhalents and secretory vessels. Though he demonstrated the anastomosis of arteries and veins, he nowhere hints his belief that the contents of the former pass into the latter, to be conveyed back to the heart, and from it to be again diffused over the body. He made a near approach to the Harveian theory of the circulation, as Harvey himself admits in his "De Motu Cordis;"[18] but the grand point of difference between Galen and Harvey is the question whether or not, at every systole of the left ventricle, more blood is thrown out than is expended on exhalation, secretion, and nutrition. Upon this point Galen held the negative, and Harvey, as we all know, the affirmative.

The famous Asclepiads held that respiration was for the generation of the soul itself, breath and life being thus considered to be identical. Hippocrates thought it was for the nutrition and refrigeration of the innate heat, Aristotle for its ventilation, Erasistratus for the filling of the arteries with spirits. All these opinions are discussed and commented upon by Galen, who determines the purposes of respiration to be (1) to preserve the animal heat; (2) to evacuate from the blood the products of combustion.

He conjectured that there was in atmospheric air not only a quality friendly to the vital spirit, but also a quality inimical to it, which conjecture he drew from observation of the various phenomena accompanying the support and the extinction of flame; and he says that if we could find out why flame is extinguished by absence of the air, we might then know the nature of that substance which imparts warmth to the blood during the process of respiration.

On another occasion he says that it is evidently the quality and not the quantity of the air which is necessary to life. He further shows that he recognized the analogy between respiration and combustion, by comparing the lungs to a lamp, the heart to its wick, the blood to the oil, and the animal heat to the flame.

From certain observations in various parts of his works, it appears that, although ignorant of the doctrine of atmospheric pressure, he was acquainted with some of its practical effects. Thus, he says, if you put one end of an open tube under water and suck out the air with the other end, you will draw up water into the mouth, and that it is in this way that infants extract the milk from the mother's breast.

Again, Erasistratus supposed that the vapour of charcoal and of certain pits and wells was fatal to life because lighter than common air, but Galen maintained it to be heavier.

He describes two kinds of respiration, one by the mouths of the arteries of the lungs, and one by the mouths of the arteries of the skin. In each case, he says, the surrounding air is drawn into the vessels during their diastole, for the purpose of cooling the blood, and during their systole the fuliginous particles derived from the blood and other fluids of the body are forced out.

He considers the diaphragm to be the principal muscle of respiration, but he makes a clear distinction between ordinary respiration, which he calls a natural and involuntary effort, and that deliberate and forced respiration which is obedient to the will; and he says that there are different muscles for the two purposes. Elsewhere he particularly points out the two sets of intercostal muscles and their mode of action, of which, before his time, he asserts that anatomists were ignorant.

He describes various effects produced on respiration and on the voice by the division of those nerves which are connected with the thorax; and shows particularly the effect of dividing the recurrent branch of his sixth pair of cerebral nerves (the pneumogastric of modern anatomy). He explains how it happens that after division of the spinal cord, provided that division be beneath the lower termination of the neck, the diaphragm will still continue to act—in consequence, namely, of the origin of the phrenic nerve being above the lower termination of the neck.