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(b. Iulis, Ceos, ca. 304 B.C.; d. Mycale)

anatomy, physiology.

Erasistratus was born into a medical family. His father, Cleombrotus, was a doctor, and his mother, Cretoxene, was the sister of the doctor Medios. Like his brother Cleophantus, Erasistratus entered the family profession. He studied medicine first in Athens as a pupil of Metrodorus, the third husband of Aristotle’s daughter, Pythias; and it was probably, at least in part, through him that he became so strongly influenced by Peripatetic thought.1 About 280 B.C he entered the university in Cos, where the medical school of Praxagoras flourished. Cos had strong political and cultural ties with Alexandria, and in that city. Erasistratus came under the influence of Chrysippus the Younger (the palace doctor of Ptolemy Philadelphus), especially in the fields of anatomy, physiology, and pathology. In his old age Erasistratus gave up medical practice and entered the Museum at Alexandria, where the unrivaled facilities afforded by the Ptolemies allowed him to devote himself to his researches. According to later tradition, an incurable ulcer on his foot caused him to commit suicide by drinking hemlock.

Erasistratus wrote a large number of works, notably on anatomy, abdominal pathology, hemoptysis, fevers, gout, dropsy, and hygiene. None of these works has survived. He is best-known for his anatomical and physiological researches. In these fields distinguished work had already been done by his immediate predecessors, Diocles and Praxagoras, and by his teachers Chrysippus and Herophilus, and the Museum itself provided highly advantageous conditions for anatomical research. The public dissection of human bodies was an innovation of the Ptolemies and remained almost exclusively the preserve of the Alexandrians. It is possible that familiarity with the Egyptian practice of embalming bodies contributed to the creation of an environment in which the dissection of the human body was not viewed with misgivings. Certain ancient authorities, notably Celsus, followed by Tertullian and St. Augustine, even accused Erasistratus of vivisecting criminals taken out of the royal prisons. Scholarly opinion is divided in its acceptance of this tradition, and Galen’s silence in the matter cannot be taken as conclusive evidence against it. It is clear from Galen that Erasistratus vivisected animals, and these dissections enabled him to draw parallels between men and beasts. For example, he made a detailed investigation of the cavities and convolutions in the brains of man, hare, and stag and correctly inferred that the number of convolutions varied with the degree of intellectual development. In addition to his ventures in comparative anatomy, Erasistratus was a pioneer in the field of pathological anatomy, conducting postmortem examinations of the bodies of men who had just died, in order to study structural changes due to morbid conditions.

As the basis for his physiology Erasistratus combined a corpuscular theory with the doctrine of the pneuma. In both these respects it seems likely that he reveals the influence of the Lyceum, where these theories played an important role. A very important factor in persuading Erasistratus to adopt the latter theory must have been the influence of such doctors as Diocles, Praxagoras, and Herophilus, in whose medical theory the pneuma doctrine plays so fundamental a role and who were themselves either directly or at least indirectly influenced by Peripatetic teachings. It is probable, too, that Erasistratus was induced to adopt his corpuscular theory by the direct influence of Strato of Lampsacus, the third head of the Lyceum and the teacher of Ptolemy Philadelphus in Alexandria shortly before Theophrastus’ death. It is perhaps worth recording that Strato also seems to have subscribed to the pneuma doctrine.2 Like Strato, Erasistratus conceived of his particles as very small, imperceptible, corporeal entities surrounded by a vacuum in a finely divided or discontinuous condition.

Upon the basis of these two theories he sought to assign natural causes to all phenomena and rejected the idea that there were hidden forces such as the power of attraction of certain organs, which many medical authors had postulated in order to explain such physiological processes as the assimilation of food and the secretion of humors. For this idea Erasistratus substituted the theory of πρός τό κ∈νουμ∈νον ακολουθiα the horror vacui, derived from Strato, whereby those empty spaces which suddenly form in the living body are continually filled.

Erasistratus may also have derived his experimental method from Strato. The Anonyrnus Londinensis (col. xxxiii) preserves some evidence of his methodology. It describes an experiment of his which anticipates another experiment, generally considered to be the beginning of the modern study of metabolism, performed in the seventeenth century by Santorio. In order to prove that animals give off certain emanations, Erasistratus recommended that a bird or similar creature should be kept in a vessel without food for some time and then weighed together with any excrement that had been passed. A great loss of weight would then be discovered.

To repair the bodily wastage which Erasistratus had so strikingly demonstrated took place not only visibly but in some part invisibly, Galen tells us that he held that Nature had provided mechanism in the form of appetites (óρέξεις)forces (δυνάμεις), and substances(üλαι), i.e., he believed that part of the purposive activity of the pneuma was the absorption of food into the body. He had made the striking discovery that all organic parts of the living creature were a tissue composed of vein, artery, and nerve (the τρυπλοκiα тω̄ν ἀγγεiων), bodies so fine that they were knowable only by reason. The vein carried the food, the artery the pneuma, and the nerve the psychic pneuma. There was no need for Erasistratus to postulate a hidden power of attraction. He held that the supply of nourishment to each particular organ took place by a process of absorption (διάδοσις) through the extremely fine pores (κενώματα) in the walls of the veins contained in it. The particles of nourishment contained in the blood were able to pass through the veins, in accordance with the principle of πρός τό κ∈νούμ∈νον ἀκολουϑiα, to fill those spaces left empty by the evacuations and emanations. Growth, then, proceeded on the principle of the accretion of like to like. Galen tells us that Erasistratus likened the growth of an animal to that of a sieve, rope, bag, or basket, since each of these grows by the addition to it of materials similar to those out of which it began to be made. The two materials which serve for the preservation of the creature, then, are blood and pneuma, the former providing the nutriment and the latter helping to transmit the natural activity.

Erasistratus rejected the widely held beliefs that digestion was a process analogous either to cooking (as Aristotle had held) or to fermentation (as Diocles had believed). He was well aware that the epiglottis closes the larynx during swallowing, thereby preventing liquids and solids from entering the trachea. He thus rejected the old and much debated belief held by Plato, Philistion, Diocles, and Dexippus that it was possible for drink to enter the lungs. He held that the food, once in the stomach, was torn to pieces by the peristaltic motion of the gastric muscles under the influence of pneuma. He gave an accurate description of the structure and function of these muscles. Unlike Diocles, he was not of the opinion that the pneuma arrived in the stomach with the food but held that it was introduced there by the gastric arteries. In accordance with this theory he sought to explain why digestion is impaired during a fever. This was due, he thought, to the impediment of the free motion of the pneuma by the blood that had penetrated into the arteries.

A portion of the food broken into pulp in the stomach was subsequently conveyed in the blood vessels to the liver, where, he believed, it was transformed into blood. Galen complains that Erasistratus did not reveal how this transformation takes place. During this process the biliary constituents are separated off and pass to the gallbladder while the pure blood from the liver is conveyed via the vena cava (κοiλη φλ∈́ψ) to the heart.

Erasistratus’ description of the vascular system and his views on the significance and structure of the heart represent a great advance over his predecessors. Some scholars have claimed that Erasistratus came near to anticipating Harvey’s discovery of the circulation of the blood, but such a claim is unwarranted. He did, however, conceive the function of the heart to be that of a pump and compared it to a blacksmith’s bellows actively dilating and contracting by its own innate force. The arteries, on the other hand, which he likened to a skin bag, were passively dilated by the pneuma forced into them by the heart’s contraction. In this respect Erasistratus rejected Herophilus’ claim, subsequently revived by Galen, that the arteries were subject to dilations and contractions synchronous with those of the heart.

Erasistratus rightly believed that both veins and arteries originated from the heart and that both of these vessels extended throughout the body, dividing into extremely fine capillaries. But, following Praxagoras, he held that only the veins contained blood, the arteries being full of pneuma. His dissections of dead animals would have confirmed this belief. He had not, however, failed to observe that the arteries of a wounded animal spurt blood. To account for this phenomenon he maintained that when an artery was severed, the escaping pneuma caused a vacuum and the pull of this vacuum (the πρός τό κ∈νούμ∈νον ἀκολουϑiα) drew blood from the veins through certain fine capillaries which were usually closed (the synanastomoses, συναναστομώσ∈ις). The blood then spurted out of the arteries after the escaping pneuma. This ingenious hypothesis was not disproved until four and a half centuries later, when Galen, who was otherwise greatly influenced by Erasistratus’ theory, showed by careful experiments in vivisection that the arteries of living beings carry blood continuously.

Erasistratus rejected the view that the pneuma was innate in the body. He believed that it was ∈̓πικτητóν, i.e., drawn in from outside through the nose and the mouth in the process of inhalation, that it passed via the bronchi to the lungs and thence through the pulmonary vein to the left ventricle of the heart. From the heart the vital pneuma was carried through the aorta ascendens and aorta descendens to the brain and to the whole body. In the brain the vital pneuma was transformed into psychic pneuma and was carried from the brain to various parts of the body by the nervous system, there to cause muscular movements by its effect upon the muscles. In order to perform this function the inspired pneuma must have a certain density. If it were too fine, it would presumably escape through pores.

The respiratory process Erasistratus held to be due to the muscular activity in the thorax. When the chest is expanded, so are the lungs, which, like the arteries, possess no motion of their own. Into the resulting empty space the outer air streams in accordance with the principle of horror vacui. The contraction of the thorax also brings about the contraction of the lungs “like a sponge compressed by the hands,” and the air is expired. The purpose of respiration, according to Erasistratus, is not to cool the innate heat, as Philistion and Diocles had believed, but to fill the arteries with pneuma. Galen provides the further information that Erasistratus declared that if the activity of the thorax were to stop, the heart would not be able to draw in any air from the lungs and suffocation would ensue.

As has already been seen, the pneuma passes from the lungs through the so-called ἀρτηρiα φλ∈βώδης, “the artery resembling a vein,” i.e., the pulmonary vein, and, with the expansion of the heart, into the left ventricle in accordance with the principle πρός τό κ∈νούμ∈νον ἀκολουϑiα. When the heart contracts, the pneuma is then driven, via the aorta, through the arteries all over the body. The return of the pneuma from the heart into the lungs is prevented by the bicuspid valve (mitral valve) and from the aorta into the heart by the semilunar (sigmoid) valves.

Since there is no possibility of any return to the lungs, any superfluous pneuma distributed throughout the arteries is, presumably, ultimately given off from the body by that process of skin respiration which Erasistratus had earlier sought to demonstrate by the experiment with the bird.

Just as the expansion of the heart led to the left ventricle’s becoming filled with pneuma, so the right ventricle becomes filled with blood which comes from the liver via the vena cava. With every contraction of the heart the blood is pumped into the lungs through the so-called φλ∈̀ψ ἀρτηριώδης “the vein resembling an artery,” i.e., the pulmonary artery, and thence, presumably, distributed by other “veins” to the rest of the organs. The return of the blood from the heart to the vena cava is prevented by the tricuspid valve and from the pulmonary artery to the heart by the semilunar valves. As is the case with the pneuma, no blood is returned to the heart; nor is there any communication between veins and arteries in the heart, the left and right ventricles being quite separate.

Erasistratus, then, wrongly attributed functions of the auricles to the two pulmonary vessels and incorrectly believed, like Galen after him, that the blood was manufactured in the liver and distributed throughout the body by the veins.

The structure of the brain is described by Erasistratus with a greater accuracy than Herophilus had achieved. Galen tells us that in his old age Erasistratus had leisure for research and made his dissections more accurate. The implication of Galen’s evidence here is that Erasistratus had not systematically examined the structure of the brain until he was an old man. As a result of these dissections he distinguished the cerebrum (∈̓γκ∈́φαλος) from the cerebellum (which he called the ∈̓π∈γκρανiς, not the παρ∈γκ∈φαλiς as Herophilus had done). He also gave a detailed description of the cerebral ventricles or cavities within the brain and of the meninges or membranes that cover the brain.

Erasistratus rejected the view of those thinkers who, like Empedocles, Aristotle, Diocles, Praxagoras, and the Stoics, had maintained that the heart was the seat of the central intelligence. In agreement with Alcmaeon, the author of the Hippocratic treatise “On the Sacred Disease,” and Plato, he placed this central organ in the brain. Herophilus had clearly shown by dissection that the nerves originated in the brain and had specified the “fourth ventricle” of the cerebellum as the seat of hegemonikon, or organ of thought. Erasistratus was most probably in agreement with this viewpoint. For, as was seen above, his observations that the cerebellum of the brain of man had more convolutions than that of other animals had led him to the conclusion that the number of convolutions varied with the degree of intellectual development.

He also agreed with Herophilus that the brain was the starting point of all the nerves. Originally he held that they sprang from dura mater (παχ∈ῑα μήνιγξ). He had discovered through vivisection that incisions into this membrane adversely affected the motor ability of living creatures. But later—probably as a result of his more accurate dissections—he succeeded in tracing the nerves into the interior of the brain and discovered the origin of each type of sensory nerve in the cerebrum.

Again in agreement with Herophilus, Erasistratus recognized the difference between sensory and motor nerves, the ν∈ῡρα αισθητικά and κινητικά (Herophilus, however, called the latter προαιρτικά). Erasistratus was of the opinion that the nerve fibers were formed “like a sail” out of three different, imperceptible strands of artery, vein, and nerve. He also believed that the nerves were filled with psychic pneuma drawn, most probably, from the ventricles of the cerebrum. The widespread belief that Erasistratus renounced this theory in his old age and maintained that the nerves contained not pneuma but marrow or brain substance3 is inaccurate and based upon a misunderstanding of the text.4 Motion, he held, was effected through the agency of the muscles, which were formed from a texture of vein, artery, and nerve. The pneuma, led to the muscles via the arteries, invested them with the capacity of synchronous expansion of length and contraction of breadth and vice versa, which resulted in the movement of the bodily parts containing them.

In pathology Erasistratus rejected the influential humoral theory or, at any rate, the abuses of this theory practiced in the school of Praxagoras. He considered research into the formation of the humors to be superfluous and, according to Galen, did not mention black bile at all in his writings. However, he could not dispense entirely with the assumption of morbid changes in the bodily humors (κακοχυμiα); he considered apoplexy, for example, to be a disease of the brain caused by an excessive secretion of cold, viscous, and glutinous humors which prevented the psychic pneuma from passing into the nerves. But the main cause of disease he held to be plethora (πληϑώρα or πλη̄ϑος τροφη̄ς), i.e., the flooding of the veins with a superfluity of blood engendered by an excessive intake of nourishment. As the plethora increases, the limbs begin to swell, then become sore, more sluggish, and harder to move. If the plethora increases still more, the superfluous blood is then discharged through the synanastomoses into the arteries, where it is compressed by the pneuma which is constantly pumped from the heart. This compressed blood collects in the extremities of the arteries and causes local inflammation (φλ∈γμονή) accompanied by fever. Moreover, since the flow of the pneuma is impeded by the presence of this blood in the arteries, it cannot perform its natural functions. As examples of diseases brought about in this way by plethora he mentions, among others, ailments of the liver, spleen, and stomach, coughing of blood, phrenitis, pleuritis, and peripneumonia.

Erasistratus’ treatment for plethora consisted primarily of starvation (ἀσιτiα), on the ground that the veins, when emptied, would more easily receive back the blood which had been discharged into the arteries. Unlike many of his contemporaries he did not resort freely to phlebotomy but employed it only upon rare occasions. Erasistratus preferred prevention to therapy and in a separate treatise stressed the importance of hygiene. In general he was opposed to violent remedies, especially purgatives, preferring in their stead carefully regulated exercise and diet and the vapor bath.

Although Erasistratus founded a school of medicine, none of his successors seems to have made any significant mark in the history of medicine. His true importance lies in the fact that he, together with Herophilus, laid the foundations for the scientific study of anatomy and physiology, and their careful dissections provided a basis and stimulus for the anatomical investigations undertaken by Galen over four centuries later.


1. There is also a strong tradition that he had heard Theophrastus himself; see Diogenes Laërtius, 5.57, and Galen, 4.729K. For the tradition linking Erasistratus with the Lyceum generally, see Galen, 2,88K; for Strato’s influence, see below.

2. See F. Wehrli, Straton von Lampsakos, die Schule des Aristoteles, V (Basel, 1950), commentary on fr. 108, p. 71; and F. Solmsen, “Greek Philosophy and the Discovery of the Nerves,” in Museum Helveticum, 18 (1961), 183.

3. See M. Wellmann, “Erasistratus,” in Pauly-Wissowa, VI, I (Stuttgart, 1907), 343; and G. Verbeke, L’évolution de la doctrine du pneuma (Paris-Louvain, 1945), p. 185.

4. With Solmsen, op. cit., p. 188.


For a collection of the evidence of Erasistratus’ views, see R. Fuchs’s dissertation Erasistratea (Leipzig, 1892). References in Galen are cited according to C. G. Kuhn, ed., Claudii Galeni Opera omnia, 20 vols. (Leipzig, 1821–1833).

See also C. Allbutt, Greek Medicine in Rome (London, 1921); H. Diels, “Über das physikalische System des Straton,” in Sitzungsberichte der Preussischen Akademie der Wissenschaften zu Berlin, 1 (1893), 101 ff.; J.F. Dobson “Erasistratus,” in Proceedings of the Royal Society of Medicine, 20 (1926–1927), 825 ff.; R. Fuchs, “De Erasistrato capita selecta,” in Hermes, 29 (1894), 171–203; W. W. Jaeger, “Das Pneuma im Lykeion,” ibid., 48 (1913), 29–72, and Scripta Minora, I (Rome, 1960), 57–102; Diokles von Karystos, die griechische Medizin und die Schule des Aristoteles (Berlin, 1938); “Vergessene Fragmente des Peripatetikers Diokles von Karystos nebst zwei Anhaengen zur Chronologie der dogmatischen Aerzteschule,” in Abhandlungen der Preussischen Akademie der Wissenschaften, Phil.-hist. Kl. 1938), no. 1–46, and in Scripta minora, II (Rome, 1960), 185–241; and “Diocles of Carystus; A New Pupil of Aristotle,” in Philosophical Review, 49 (1940), 393–414, and in Scripta minora, II, 243–265; W.H.S. Jones, The Medical Writings of Anonymus Londinensis (Cambridge, 1947); I. M. Lonie, “Erasistratus, the Erasistrateans and Aristotle,” in Bulletin of the History of Medicine, 38 (1964), 426–443; F. Solmsen, “Greek Philosophy and the Discovery of the Nerves,” in Museum Helveticum, 18 (1961), 150 ff.; F. Steckerl, The Fragments of Praxagoras of Cos and His School (Leiden, 1958); G. Verbeke, L’évolution de la doctrine du pneuma (Paris-Louvain, 1945); F. Wehrli, Straton von Lampsakos, die Schule des Aristoteles, V (Basel, 1950); M. Wellmann, “Erasistratus,” in Pauly-Wissowa, VI, 1 (Stuttgart, 1907), 333–350; and L. G. Wilson, “Erasistratus, Galen, and the Pneuma,” in Bulletin of the History of Medicine, 33 (1959), 293–314.

I am grateful to the University of Newcastle upon Tyne Research Fund for a grant which enabled me to consult works in London libraries.

James Longrigg

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Erasistratus (304 BC-250 BC) is best known for his works on human cadavers and his knowledge of the human body. He is considered the father of physiology.

Erasistratus, considered the father of physiology, was born on the island of Chios in ancient Greece, to a medical family. His father and brother were doctors, and his mother was the sister of a doctor. He studied medicine in Athens and then, around 280 B.C., enrolled in the University of Cos, a center of the medical school of Praxagoras. Erasistratus then moved to Alexandria, where he taught and practiced medicine, continuing the work of Herophilus. In his later years, he retired from medical practice and joined the Alexandrian museum, where he devoted himself to research.

Although Erasistratus wrote extensively in a number of medical fields, none of his works survive. He is best known for his observations based on his numerous dissections of human cadavers (and, it was rumored, his vivisections of criminals, a practice allowed by the Ptolemy rulers). Erasistratus accurately described the structure of the brain, including the cavities and membranes, and made a distinction between its cerebrum and cerebellum (larger and smaller parts). He viewed the brain, not the heart, as the seat of intelligence. By comparing the brains of humans and other animals, Erasistratus rightly concluded that a greater number of brain convolutions resulted in greater intelligence. He also accurately described the structure and function of the gastric (stomach) muscles, and observed the difference between motor and sensory nerves. Erasistratus promoted hygiene, diet, and exercise in medical care.

In his understanding of the heart and blood vessels, Erasistratus came very close to working out the circulation of the blood (not actually discovered until William Harvey in the seventeenth century A.D.), but he made some crucial errors. Erasistratus understood that the heart served as a pump, thereby dilating the arteries, and he found and explained the functioning of the heart valves. He theorized that the arteries and veins both spread from the heart, dividing finally into extremely fine capillaries that were invisible to the eye. However, he believed that the liver formed blood and carried it to the right side of the heart, which pumped it into the lungs and from there to the rest of the body's organs. He also believed that pneumapneuma, a vital spirit, was drawn in through the lungs to the left side of the heart, which then pumped the pneuma through the arteries to the rest of the body. The nerves, according to Erasistratus, carried another form of pneuma, animal spirit.

After Erasistratus, anatomical research through dissection ended, due to the pressure of public opinion. Egyptians believed in the need of an intact body for the afterlife—hence mummification. Real anatomical studies were not resumed until the thirteenth century. □

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Erasistratus (ĕrəsĬs´trətəs), fl. 3d cent. BC, Greek physician, b. Chios. He was the leader of a school of medicine in Alexandria, and his works were influential until the 4th cent. AD He considered plethora (hyperemia) to be the primary cause of disease. As opposed to the then current belief in the humors, he suggested that air carried from the lungs to the heart is converted into a vital spirit distributed by the arteries. He developed a reverse theory of circulation (veins to arteries). Studying from dissections, he observed the convolutions of the brain, named the trachea, and distinguished (as did his contemporary Herophilus) between motor and sensory nerves. He also devised a catheter and a calorimeter.