Читать книгу The Greatest Benefit to Mankind: A Medical History of Humanity - Roy Porter - Страница 24

Aristotle’s royal pupil, Alexander, routed all his rivals, lamented there were no more worlds to conquer, and expired in 323 BC, supposedly exclaiming, ‘I die by the help of too many physicians.’ His destruction of the Persian Emperor Darius III had brought Egypt within the hellenistic sphere of influence, and after Alexander’s death science gained a prominent place at the court of King Ptolemy, who ruled from 323 to 282 BC and established his capital at Alexandria, at the mouth of the Nile.

King Ptolemy’s main cultural creations, the Alexandrian Library and the Museum (sanctuary of the Muses) installed Greek learning in a new Egyptian environment: Archimedes, Euclid and the astronomer Ptolemy were later to teach there. The library became a wonder of the scholarly world, eventually containing, it was said, 700,000 manuscripts, and its facilities included an observatory, zoological gardens, lecture halls and rooms for research.^*

Thanks to Alexander’s conquests, the hellenistic world stretched from the Persian Gulf to Sicily, with Greek becoming the lingua franca of the elite. One consequence was a remarkable increase of new information on animals, plants, minerals and drugs. Alexandria also attracted medical talent, notably Herophilus of Chalcedon (c. 330–260 BC and his contemporary, Erasistratus of Ceos (c. 330–255 BC). Their writings having been lost, we know about them only through later physicians. Cornelius Celsus (fl). AD 60 reported that they dissected, or at least experimented upon, living humans, which is not inconceivable, for Greeks may have used their privileged status in Alexandria to experiment on their inferiors, especially condemned criminals.

Herophilus was apparently a student of Praxagoras of Cos (fl. 340 BC), who had improved Aristotelian anatomy by distinguishing arteries from veins. Praxagoras saw the arteries as air tubes, similar to the trachea and bronchi, conducting the breath of life (pneuma) from the lungs to the left side of the heart and thence through the aorta and other arteries to the whole body. The arteries stemmed from the heart; the veins, by contrast, Praxagoras believed, arose from the liver, their function being to carry the blood, created from digested food, to the rest of the body. The combining of blood and pneuma generated innate heat.

Herophilus practised medicine in Alexandria under the first two Ptolemies, apparently dissecting human cadavers in public. He wrote at least eleven treatises. Three were on anatomy: it was he who discovered and named the prostate and the duodenum (from the Greek for twelve fingers, the length of gut he found). He also wrote on the pulse as a diagnostic guide, on therapeutics, ophthalmology, dietetics and midwifery, and a polemic ‘Against Common Notions’.

Continuing Praxagoras’ differentiation between veins and arteries, Herophilus pointed out that the coats of the arteries were much thicker than those of the veins. Unlike Praxagoras, however, he held that the arteries were filled not with air but with blood. His most striking dissection feat was the delineation of the nerves. Demonstrating their source in the brain enabled him to conclude that they played the part preceding thinkers had ascribed to the arteries: transmitting motor impulses from the soul (intelligence centre) to the extremities. Rebutting Aristotle, he thus established the importance of the brain, distinguishing the cerebrum from the cerebellum and displaying the nerve paths from the brain and spinal cord. His description of the rete mirabile, the network of arteries at the base of the brain, shows he dissected animals as well as human corpses, since it does not exist in humans.

Herophilus also devoted attention to the liver and to ‘veins’ ending in glandular bodies which, he believed, nourished the intestines but did not pass to the liver. These ‘veins’ must have been the lacteals or chyle-vessels, whose function was explained by Aselli some two thousand years later. Praxagoras’ interest in the pulse was taken up by Herophilus. Identifying pulsation as derived from the heart, he developed a speculative classification of different classes of pulse, on the basis of magnitude, strength, rate and rhythm, and is reputed to have tried to calculate pulse by means of a portable water clock.

Erasistratus is far more nebulous and controversial. He supposedly studied medicine in Athens before settling in Alexandria, where he experimented on living animals and perhaps humans. His main discoveries concerned the brain which, like Herophilus but unlike Aristotle, he regarded as the seat of intelligence. He too distinguished the cerebrum from the cerebellum, described the cerebral ventricles within the brain, and distinguished between motor and sensory nerves. Nerves were hollow tubes containing pneuma (‘spirit’ or air), which transmitted sensation, enabling muscles to produce motion.

In a tradition going back to Alcmaeon, he also believed that pneuma alone – not blood – was contained in the arteries: it was taken in through the lungs, piped to the heart (which he compared to a blacksmith’s bellows) and then pumped out to fill the arteries. Blood by contrast was formed in the liver and carried by the veins. Why then was it blood that spurted from a cut artery? It was drawn in, Erasistratus reasoned, because nature abhorred a vacuum.

Erasistratus has been portrayed as an early mechanist, because of his model of bodily processes: digestion for instance involved the stomach grinding food. Yet this may be a caricature created by Galen for polemical purposes. Even Galen applauded his remarkable investigations of brain anatomy, while being scathing about his other views, particularly the idea that the arteries contained air alone. Erasistratus was clearly a radical; for want of evidence, he is also a riddle.

In the following centuries medicine, like philosophy, split into sects: Hippocratics, Herophileans and Erasistrateans were later challenged by the Pneumatists, who regarded pneuma as a fifth element which flowed through the arteries, sustaining vitality. All such sects were later given the label of ‘rationalist’, to signal their antagonism to the Empirics, a band of physicians led by Heraclides of Tarentum (fl. 80 BC), who spurned medicine based on speculation about hidden disease causes in favour of one grounded on experience. What mattered, Empirics claimed, was not cause but cure, and so they collected case histories and remedies. Knowledge, they held, could be better gained at the bedside than by dissection; what counted was which drugs worked. Hence theory must bow to experience – a claim later opponents, principally Galen, rejected as shallow.