Notes

PRECISE dates in the life of Erasistratus cannot be ascertained. Tradition points to the conclusion that he was living and working in Alexandria at about the same time as Herophilus, of whom perhaps he was a slightly younger contemporary. This would place him in the first half of the third century B.C. We have the titles of many of his works. The writings themselves are lost; even to Galen (died A.D. 201), from whom we draw most of our information concerning Erasistratus, only extracts were accessible.'

Like Herophilus, Erasistratus divided his time between professional practice and research, and like him was interested particularly both in anatomy and physiology. But while Herophilus, in addition to a wide general knowledge of medicine, had a particular bent for anatomy, the trend of the researches of Erasistratus leads us to class him primarily as a physiologist. A noticeable feature of his work was an attempt at scientific consistency. His earlier studies had brought him into contact with the Peripatetics; indeed tradition represents him as working at one time under Theophrastus (c. 372-287 B.C.), himself the pupil of Aristotle. In this school he may have been introduced to the physical theory of Democritus (c. 400 B.C.). Erasistratus accepted in general the atomic theory that is associated with the name of Democritus, but modified it in a manner peculiar to himself. He attempted, not without success, to harmonize it with his phvsiological system. Democritus had hypothecated a continuous void or vacuum but Erasistratus assumes a discontinuous vacuum. He believes in the existence of innumerable minute empty spaces interspersed with the atoms in the human body. Observing the continued subdivision of certaln vessels, he argues that they must eventually decrease in size beyond the limits of human vision.

Philosophically, Erasistratus has an objection to hidden causes, the only one which he admits being what he calls Physis, which we may here translate Nature. He could not wholly dismiss a creative force, but he attempted to reduce her activities to this simple term. In contrast to his contemporaries who explained certain bodily activities by the 'o'XcK (attractive power) of the organs, Erasistratus brings into play the assumed tendency of Nature to fill a void-adcoXov9za 'npos TO KCEVoV,aEvoV which we may represent by horror vacui. This doctrine was held in opposition to that of Empedocles (c. 500 B.C.), who claimed that" Love and Hate," i.e., attractive and repulsive forces, were responsible for the formation of the universe.

I shall endeavour to put together such fragments as set forth the biological views and discoveries of Erasistratus. These may be considered under two headings, first as to the growth and structure of the organs, and secondly as to their functions. The discussion of these will be followed by an account of the teaching of Erasistratus on pathology, on the humoral theory and on practical medicine.

(II) GROWTH AND STRUCTURE.

Nowadays all men of science and many who cannot claim that proud title are familiar with the word metabolism.1 In the fourth century B.C., not only the term, but its connotation, were unrecognized. Yet Erasistratus evidently had some inkling of the process. The exact words which he used to describe the process are unknown, but Galen bas preserved for us his own representation of the teaching of Erasistratus, which he endeavours to represent in as ridiculous a light as possible. Nevertheless we can see dimly through Galen's quotations something of the real Erasistratus.


Galen II, 87.' " The heart is at first no larger than a millet seed, or, if you like, a bean. Ask yourself how it could grow large otherwise than by being distended and receiving nutriment throughout its whole extent, just as we have shown above that the seed is nourished. But even this is unknown to Erasistratus, who makes so much of Nature's art. He supposes that animals grow just like a sieve, a rope, a bag, or a basket, each of whicl grows by the addition to it of materials similar to those out of which it began to be miade."

To add a mesh to a net, or a fresh row to a knitted bag, seems to me a fitting metaphor to describe the accretion of new cells on an already existing cell. Though our physiologist, living before the age of microscopes, could have had no knowledge of cellular tissue, I imagine that he was led to his theory by observation of some such phenomenon as the growth of the bulb of a monocotyledon such as that of his native asphodel, a word which, being transformed, has become our daffodil

As there is a natural tendency to growth, so there is, in the course of nature, a constant wastage. This takes place partly by visible means, e.g., by the various known forms of atttrition and excretion, partly by imperceptible processes only cognizable by reason.

" To repair the waste, Nature, according to Erasistratus, has provided mechanism in the form of instincts or appetites (opfs'tcs), substances (Oxal) and forces (8Uva4eLs). The chief of the last named is the power of the pneuma, which transmutes the nourishment into a form suitable for supplying the place of the inatter carried off (fsS a3yavA+;pwoav -ca' 6ocPpo¢S4OfWV)."3 This recalls the doctrine of Heraclitus of the constant flux and transmutation of one subject into another.

Erasistratus was among the first to recognize the division of the nerves as motor and sensory, though the discovery is sometimes claimed for Herophilus

It was Erasistratus who first derived the sensory nerves, which he regarded as hollow, from the meninges, the motor nerves from the brain and cerebellum. Later, however, he traced all nerves to the brain,4 which, he says, appears to be the origin of the bodily functions, for the perforations of the nostrils and the ears were found to be connected with the brain, and processes from the brain lead also to the tongue and the eyes.5 " He also," says Galen, " wrote accurately about its four ventricles."

Erasistratus described the vasa chylifera of the mesentery,' but cannot have all the credit for their discovery, as Herophilus had probably preceded him in distinguishing from the veins of the mesentery certain vessels ending in glands.' He certainly did not understand their function, but thought them to be a kind of artery containing first pneuma and then chylos. Erasistratus is said to have first observed them when dissecting new-born kids.

Herophilus had made some comparisons of the organs of man with those of certain animals. Erasistratus extended these comparative studies to the brain. He observed that the surface of this organ presented greater complexity in man. This greater complexity, he inferred, was the reason of man's superiority in intelligence over the brute creation in general.' He described the brain with more accuracy than Herophilus,2 noticing not only the two lateral ventricles and the third ventricle, but also the fourth ventricle under the cerebellum, communicating with the third.3

Perhaps the greatest contribution of Erasistratus to Anatomy was his appreciation of the nature of bodily tissue, implied in the following passages:

" He says that the coats of the arteries and generally of all parts of the creature are a tissue of (7r-7weX8at fK) vein, artery and nerve, and each part is nourished by the vein contained in it, namely, the simple vein apprehensible by reason (A&yew OewprrTris)." 4

And again, " The nerve contains veins and arteries in itself like a rope formed by plaiting three strands of different kind.

He did not, however, push this theory to extremes, and for want of a better explanation he described certain parts of the body as being a " deposit of nutriment " (7rap6'yxu/Aa Tpoopis), classifying under this head the brain, marrow, liver, and spleen.6

In knowledge of structure of the lungs and the digestive organs it does not appear that Erasistratus made any advance on his predecessors. He was content to take the current accounts of them and to investigate rather their functions than their conformation.


(III) BODILY FUNCTIONS.

We shall now consider the chief processes by which life is supported in the animal.

(a) Digestion.
With regard to digestion Erasistratus was a reactionary. The majority of his contemporaries considered the process to be akin to cooking or coction (7r6* st), the chief or only agent being the "innate heat" of the body. He entirely rejected this theory,' and preferred to make it for the most part a mechanical process. The food, he believed, is ground by the muscular action of the stomach itself-a peristaltic movement of the muscular coat helped by the pneutmah which has entered the stomach through the arteries, and not with the food itself, as was believed by his Athenian predecessor, Diokles of Karystos (fl. c. 350 B.C.). It is interesting to observe that an exactly similar controversy took place among the physiologists of the seventeenth and eighteenth centuries.

It would seem that in the view of Erasistratus the function of the pneuma is here entirely mechanical. Probably it only serves in some way to originate the motion, for Erasistratus criticized the opinion of Pleistonikos and Diokles that the pneumna sets up a kind of fermentation or decomposition of the food in the stomach.9 His remark that fever produces indigestion because the energy of the pneuma is then impeded, is consistent with this view.

When the trituration is complete, the chylos is passed on from the stomach and intestines to the liver, where, by some unexplained process, it is transformed into blood.' Pure blood passes thence to the heart through the vena cava. At every diastole the biliary constituents are separated off and pass to the bile-duct,2 any stoppage of which produces jaundice.' The blood passes from the heart through the pulmonary vein to the lungs.

(b) Respiration.
Digestion then is partly due to the pneumia, the earlier history of which must be now considered.

Erasistratus is quite clear (in opposition to the author of the Aristotelian De spiritu and others) that there is no innate breath in the body-the pneuma, is ?7rLKr77Tn%, i.e., derived from outside. Actually we hear that it is drawn, in the process of inhalation, from the outside air by the nose and mouth. It passes by the bronchi (Tp6JTat apT-Piai) to the lungs; and thence through the pulmonary vein to the left ventricle of the heart,4 and thence further by the arteria ascendens and arteria descenden8 to the brain and to the whole body. The process by which the zotic pneuma (" vital spirit " of later writers) of the heart becomes psychic pneumna (" animal spirit " of later writers) in the brain remains a mystery.'

The pneuma inhaled must have a certain density for otherwise suffocation would ensue. He instances cases of suffocation due to the inhalation of the vapour produced by pouring water on glowing cinders, i.e., by carbon monoxide.6 It is the entry of pneiuna into the muscles that causes themn to expand. For this it must have sufficient density, for if too fine it would presumably escape through pores.7 The pneuma, like the blood, can only flow one way; the bicuspid valves prevent it from returning from the heart into the lung; the sigmoid valves of the aorta prevent its return into the heart.'
(c) Vasctlar System.
The aorta, Erasistratus considered, divides into arteries, which again divide and subdivide beyond the limits of vision. Veins and nerves are similarly divided, and every organ is built up of a system, or rather network, of vein, artery, and nerve. These minute tubes " plaited together " form tissue. Through these tubes-for the nerves also are tubes-blood, essential for nourishment, and pneuma, of two kinds, necessary for motion and sensation, are conveyed to every part.

We have referred above, under the headings (a) Digestion and (b) Respiration, to the motion of the blood from liver to heart and thence to lungs, and, presumably, by various veins from the heart to other organs; and also to the motion of the pneuma from lungs to heart and thence through the aorta to various arteries and so to the organs. The left and right cardiac ventricles, the repositories of pneuma and blood respectively, are quite separate, so that there is no communication between veins and arteries in the heart. At the other end of the vascular system both pneuma and blood have been used up by the processes of nutrition or voided by excretion, so that there is nothing left to be returned to the heart.9

It is generally stated (e.g. by Allbutt,1' Singer"1 and others) that Erasistratus came near to anticipating Harvey's discovery of the circulation of the blood by eighteen centuries. This is perhaps to claim rather too much for him. We may, however, note the following significant points.

(a) He had a fairly clear conception of the function of the heart as a pump. In this he was opposed by Galen who, following Herophilus, believed that the arteries are subject to dilatation and contraction owing to being closely connected, apparently by some nervous process, with the heart, so that their motions are simultaneous and identical with the motions of that organ. Erasistratus on the other hand asserts that the heart is filled because it becomes dilated, but the arteries are dilated because they are filled.' Erasistratus compares the heart to the blacksmith's bellows, the arteries to a skin bag.2 The heart, then, according to Erasistratus actively dilates and contracts by its own innate force (&vvaFut). The arteries, on the other hand, are passively dilated, owing to the stream of pneutma forced into them by the heart's contraction. They contract, presumably, by their own elasticity. The pneutma cannot regurgitate into the heart owing to the sigmoid valves.
(b) (b) Arteries and veins are connected in the following manner: " Arteries and veins are continually divided into smaller and more numerous vessels and are carried all over the body; for there is no point at which there is not the termination of some vessel. The ends are such fine points that by the closing of their extreme orifices the blood is confined within them. Thus, though the orifices of vein and artery are very close to each other, the blood remains within its own bounds (i.e., the veins) and at no point encroaches on the breath-vessels (i.e., the arteries)." B These final orifices are the synanastoMoses. Thus, he realized the existence of connexions between veins and arteries, through which blood might pass, though under normnal circumstances he held that it did not so pass. (c) The heart, however, he considered, was the origin of both sets of vessels.4 (d) It is sometimes stated that Erasistratus had some knowledge of the pulmonary circulation. The opinion is based on the following passage:
" From' the artery which lies along the spine there are branchings (apophyses) of vessels along each rib, right and left alike ; these being still further subdivided (and dispersed) into the adjacent parts terminate in branches imperceptibly small. When, therefore, any blood falls into these arteries, it sometimes rises (AaU8advEL TR1V a6acpopcv) by the hollow vein into the neighbourhood of the lung and also by the connexions by which the lung is attached to the artery along the spine; for thus blood which has entered (the artery) finds its way back to the lung by this way also."