Galen’s injunctions on the correct way to practise medicine are ubiquitous. They range in length from a few lines to whole books, and are directed to patients and doctors of greater maturity and experience as well as to those embarking on a medical career. Their message, that one should follow Galen’s advice and example as a Hippocratic physician, is constantly reinforced by instances of his successful intervention or of the failure of others. Time and again he emphasised that it was not enough simply to have read the right books and have gained a theoretical understanding of medicine; this must be supplemented by practical expertise, which reinforced, and was in turn reinforced by, philosophy. Indeed, his sympathies at times were far more with the approach of the Empiricists, with their store of practical information, than with those who put forward theories, however intellectually exciting, based on little or no acquaintance with the facts of medical life.1 Galen strove for a unified art of medicine, in which the effective treatment of the sick depended on a profound understanding of the body coupled with a broad acquaintance with all types of therapy. Although he acknowledged the existence of specialists, particularly in big cities such as Rome and Ephesus, the practitioners for whom he wrote were of necessity generalists and were required to know how all the constituent parts of the medical art came together.2 At the base of Galen’s medicine lay his conviction of the supreme importance of anatomy. An ignorant incision could easily result in the death of the patient, and a misunderstanding of the pathways of the nerves could delay or frustrate a cure.3 But considerations of medical prudence and practical utility were only part of Galen’s justification for anatomy. In his opinion, only through dissection could one gain a proper understanding of the organisation and workings of the body, in sickness and in health. To this end, he wrote a variety of treatises on anatomical themes, ranging from short elementary tracts on bones, nerves, veins, arteries and muscles to a big manual of dissection, Anatomical Procedures.4 He repeated his conclusions in two other large treatises aimed at showing the value of anatomy for philosophers interested in the human body. In On the Use of Parts he discussed his discoveries in Aristotelian terms, whereas in On the Opinions of Hippocrates and Plato he

defended Plato’s ideas on physiology and psychology against the Stoics.5 Both here and in his discussions elsewhere on the Timaeus he argued that Plato was well acquainted with contemporary medical theory, even if few scholars today would agree with him that Plato’s teleological anatomy depended on the teachings of Hippocrates.6 But no amount of book learning or theoretical understanding could replace actual dissection for fixing in one’s mind all the details of the human body.7 Practice, and still more practice, was essential. The failure of an ‘excellent Empiricist’ to save the life of a schoolboy who had been jabbed in the arm by a sharp stylus is turned by Galen into a cautionary tale of how, even if one had read everything available on anatomy, one might not fully understand the tiny details of the nervous system that only dissection could reveal. Even then, one might have to repeat the process several times before one had really grasped all that was thereby revealed.8 How one should perform a dissection was specified at length in Anatomical Procedures and in two other treatises, now lost in Greek but known in Arabic, that dealt with the practical details of dissection and vivisection.9 Galen was well aware that it was impossible to carry out systematic dissections on human bodies; gazing at a skeleton or at the surface anatomy of a slave was all that was done even in the best medical schools.10 But that should not prevent one from taking advantage of what chance had placed in one’s way – a corpse stripped bare when the tomb in which it lay had been opened to view by a flood, an executed criminal hanging on a gibbet or the bodies of dead Germans that littered the battlefield after one of the victories of Marcus Aurelius.11 The wise practitioner would also profit from the cases brought to him to gain experience of the internal organisation of the body. Above all, one could experiment on animals, both living and dead. Galen was conscious of the problem of extrapolating from animals to human beings, often warning his audience about drawing rash conclusions solely from animal dissections, but he could do little else, even if it led him into errors at times.12 His human womb has cotyledons like that of a ruminant; his thyroid cartilage is that of a pig; and his belief that the left kidney was lower in the body than the right is true of apes, but not humans.13 However, animal dissection also had advantages, not least in allowing experimentation on living bodies as well as dead. The sudden cessation of the loud squeals of a pig when the free passage of nerves along the spinal cord was interrupted by ligation or cutting could not fail to have a powerful effect on the audience. Although he also recommended sheep and goats as good subjects for public dissections, Galen preferred to use monkeys, such as the Barbary ape, on the grounds that they most resembled man.14 But the look of pain on the face of a monkey being vivisected might be too much to bear, and sheep, pigs and goats could serve just as well at times.15 Galen seems to have taken advantage of whatever came his way. On one occasion he even managed to obtain from the emperor’s cook the heart of an elephant, which he began to dissect in order to

see whether there was a bone in the middle. Finding a bony structure there, he concluded that such huge beasts did indeed have a bone in the heart. He was not to know that in elderly elephants the fibrous triangles separating the aorta and the ventricles often ossify and give the impression of a bone.16 His daily dissections, some at first in public, not only gave him the necessary dexterity for his surgical interventions but also enabled him to go beyond what the Alexandrians and his immediate predecessors had done.17 His descriptions of many of the bones of the body would be acceptable today, and his errors in his reports of the heart and vascular system are far more the result of working with animals and of mistaken interpretation than of incompetent dissection. His studies of the nerves and muscles are remarkably accurate, especially given that they were performed without modern aids and involved at times structures that are hard to see with the naked eye. He made important discoveries concerning the ducts of the sublingual glands, the Achilles tendon (although his description more closely resembles the tendon in monkeys) and the muscles of the face. He was prepared to change his views if presented with new anatomical evidence. The muscles that flex the first joint of each finger and toe, the musculi interossei, were for a long while unknown to him, but were described at length in books from the mid-160s onwards, On the Anatomy of Muscles, On the Use of Parts and Anatomical Procedures.18 His descriptions of the nerves are particularly impressive. In a complex and difficult series of experiments he traced the pathways of the nerves from inside the brain and down the spinal cord, identifying in the process the recurrent laryngeal nerve and establishing the relationship between the intercostal muscles and nerves in producing the voice.19 It is a substantial list of discoveries, comparable in extent, as far as we can tell, only with those made much earlier by Herophilus and Erasistratus.20 Galen used his anatomical experiments to find solutions to many problems posed by his predecessors.21 So, for example, he refuted Asclepiades’ ideas on the functions of the bladder and ureters by a series of dissections that proved that urine flowed in one direction only.22 This tradition of anatomical demonstration he traced back to Hellenistic times, if not to Hippocrates himself.23 He repeated Erasistratus’ experiments on blood flow, inserting a cannula into an artery to see whether pulsation continued beyond the cannula, and what happened if the artery was ligated.24 He vivisected the heart and lungs to see the beating of the heart and arteries and to investigate what would happen if one constricted the heart.25 His erroneous conclusion that the pulse itself was a movement contained within the coats of the arteries, not the result of blood forced by the heart into the arteries, may be excused by the difficulty of performing such an experiment without the help of modern technology.26 These dissections confirmed Galen in his view that the body consisted anatomically of three near-separate systems. Whether they developed simultaneously from the very first stages of the foetus or whether the heart or, as he came to believe at the end of his life, the liver was formed first was a difficult question, even when investigated by careful dissection along the

lines pioneered by Aristotle.27 But Galen rejected the Aristotelian and Stoic view of the primacy of the heart as the seat of the controlling power of the body, insisting time and again that the results of his dissections proved that Plato was right to believe that the liver, the heart and the brain were the origins of three parallel systems, each of which had a different function.28 The liver was responsible for nutrition. In the liver ‘digested’ or ‘concocted’ food received from the stomach and intestines was turned into nutritious blood, which was then transported within the veins to provide the essential nutriment for all the body.29 Every living being, plants as well as animals, was provided by the Creator with the four ‘natural faculties’ of attraction, assimilation, excretion and growth. Each part of the body had thus the potentiality, as a result of its elemental organisation, to feed on this nutritious blood, to assimilate whatever it needed to grow and to function, and to excrete potentially harmful residues that it no longer needed.30 The body was a living universe, responding to changes and actively seeking whatever it needed in order to exist and to function. Galen’s vitalist approach thus contrasted with the mechanistic understanding of the body proposed by Erasistratus and Asclepiades, in which, for instance, the excretion of residues through the kidney and bladder did not require any active participation from the organs themselves but only obedience to the laws of physics.31 The nutritious venous blood, produced in the flesh of the liver, was attracted into the various parts of the body as each required.32 Some of the venous blood that reached the right side of the heart then passed through perforations in the intraventricular septum to the left side, where it joined refined air, pneuma, coming from the lungs via the pulmonary vein. Galen was aware that the pulmonary artery carried blood from the heart to the lungs and that some of this blood returned in the pulmonary vein, but he seems to have regarded this means of transit as secondary to that via the septum.33 He may have been strengthened in this belief by his discovery that in the foetus there is a direct connection between the two sides of the heart via the ductus arteriosus and the foramen ovale, which closes at birth, and by his correct observation of pittings within the actual septum. It would have been simple for Galen to conclude that one connection replaced the other after birth, although he himself never states this.34 Similarly, although he accepted Erasistratus’ view that the arterial and venous systems were linked by invisible capillaries, he considered that they allowed only for the transfer of a small amount of nutritious venous blood and pneuma between the two systems, and were fully opened only in unusual or abnormal circumstances.35 Although Galen provided much of the anatomical data on which, fifteen centuries later, William Harvey was to base his theory of the circulation of the blood, Galen’s own discoveries in no way entailed that conclusion, and they could be easily explained by his own physiological theories.36 Given his conviction of the separate functions of his three systems, Galen was hardly likely to have searched diligently for a means to unify only two of the three into a single circulation of the blood.