The 100 Most Influential Scientists of All Time (5 page)

Galen regarded anatomy as the foundation of medical knowledge, and he frequently dissected and experimented on such lower animals as the Barbary ape (or African monkey), pigs, sheep, and goats. Galen's advocacy of dissection, both to improve surgical skills and for research purposes,
formed part of his self-promotion, but there is no doubt that he was an accurate observer. He distinguished seven pairs of cranial nerves, described the valves of the heart, and observed the structural differences between arteries and veins. One of his most important demonstrations was that the arteries carry blood, not air, as had been taught for 400 years. Notable also were his vivisection experiments, such as tying off the recurrent laryngeal nerve to show that the brain controls the voice, performing a series of transections of the spinal cord to establish the functions of the spinal nerves, and tying off the ureters to demonstrate kidney and bladder functions. Galen was seriously hampered by the prevailing social taboo against dissecting human corpses, however, and the inferences he made about human anatomy based on his dissections of animals often led him into errors. His anatomy of the uterus, for example, is largely that of the dog's.

Galen's physiology was a mixture of ideas taken from the philosophers Plato and Aristotle as well as from the physician Hippocrates, whom Galen revered as the fount of all medical learning. Galen viewed the body as consisting of three connected systems: the brain and nerves, which are responsible for sensation and thought; the heart and arteries, responsible for life-giving energy; and the liver and veins, responsible for nutrition and growth. According to Galen, blood is formed in the liver and is then carried by the veins to all parts of the body, where it is used up as nutriment or is transformed into flesh and other substances. A small amount of blood seeps through the lungs between the pulmonary artery and pulmonary veins, thereby becoming mixed with air, and then seeps from the right to the left ventricle of the heart through minute pores in the wall separating the two chambers. A small proportion of this blood is further refined in a network of nerves at the base of the skull (in reality found
only in ungulates) and the brain to make psychic pneuma, a subtle material that is the vehicle of sensation. Galen's physiological theory proved extremely seductive, and few possessed the skills needed to challenge it in succeeding centuries.

Building on earlier Hippocratic conceptions, Galen believed that human health requires an equilibrium between the four main bodily fluids, or humours—blood, yellow bile, black bile, and phlegm. Each of the humours is built up from the four elements and displays two of the four primary qualities: hot, cold, wet, and dry. Unlike Hippocrates, Galen argued that humoral imbalances can be located in specific organs, as well as in the body as a whole. This modification of the theory allowed doctors to make more precise diagnoses and to prescribe specific remedies to restore the body's balance. As a continuation of earlier Hippocratic conceptions, Galenic physiology became a powerful influence in medicine for the next 1,400 years.

Galen was both a universal genius and a prolific writer. About 300 titles of works by him are known, of which about 150 survive wholly or in part. He was perpetually inquisitive, even in areas remote from medicine, such as linguistics, and he was an important logician who wrote major studies of scientific method. Galen was also a skilled polemicist and an incorrigible publicist of his own genius, and these traits, combined with the enormous range of his writings, help to explain his subsequent fame and influence.

Galen's writings achieved wide circulation during his lifetime, and copies of some of his works survive that were written within a generation of his death. By 500 CE his works were being taught and summarized at Alexandria,
and his theories were already crowding out those of others in the medical handbooks of the Byzantine world. Greek manuscripts began to be collected and translated by enlightened Arabs in the 9th century, and in about 850 Hunayn ibn Ishāq, an Arab physician at the court of Baghdad, prepared an annotated list of 129 works of Galen that he and his followers had translated from Greek into Arabic or Syriac. Learned medicine in the Arabic world thus became heavily based upon the commentary, exposition, and understanding of Galen.

Galen's influence was initially almost negligible in western Europe except for drug recipes, but from the late 11th century Hunayn's translations, commentaries on them by Arab physicians, and sometimes the original Greek writings themselves were translated into Latin. These Latin versions came to form the basis of medical education in the new medieval universities. From about 1490, Italian humanists felt the need to prepare new Latin versions of Galen directly from Greek manuscripts in order to free his texts from medieval preconceptions and misunderstandings. Galen's works were first printed in Greek in their entirety in 1525, and printings in Latin swiftly followed. These texts offered a different picture from that of the Middle Ages, one that emphasized Galen as a clinician, a diagnostician, and above all, an anatomist. His new followers stressed his methodical techniques of identifying and curing illness, his independent judgment, and his cautious empiricism. Galen's injunctions to investigate the body were eagerly followed, since physicians wished to repeat the experiments and observations that he had recorded. Paradoxically, this soon led to the overthrow of Galen's authority as an anatomist. In 1543 the Flemish physician Andreas Vesalius showed that Galen's anatomy of the body was more animal than human in some of its aspects, and it became clear that Galen and
his medieval followers had made many errors. Galen's notions of physiology, by contrast, lasted for a further century, until the English physician William Harvey correctly explained the circulation of the blood. The renewal and then the overthrow of the Galenic tradition in the Renaissance had been an important element in the rise of modern science.

(b. 980, Bukhara, Iran—d. 1037, Hamadan)

A
vicenna (Arabic: Ibn Sīnā) was an Iranian physician and the most famous and influential of the philosopher-scientists of Islam. He was particularly noted for his contributions in the fields of Aristotelian philosophy and medicine. He composed the
Kitāb al-shifā' (Book of Healing
), a vast philosophical and scientific encyclopaedia, and
Al-Qānūn fī al-tibb (The Canon of Medicine
), which is among the most famous books in the history of medicine.

Avicenna's
Book of Healing
is probably the largest work of its kind ever written by one man. It discusses logic, the natural sciences, including psychology, the
quadrivium
(geometry, astronomy, arithmetic, and music), and metaphysics, but there is no real exposition of ethics or of politics. His thought in this work owes a great deal to Aristotle but also to other Greek influences and to Neoplatonism.

The Canon of Medicine
is the most famous single book in the history of medicine in both East and West. It is a systematic encyclopaedia based for the most part on the achievements of Greek physicians of the Roman imperial age and on other Arabic works and, to a lesser extent, on his own experience (his own clinical notes were lost during his journeys). Occupied during the day with his duties at court as both physician and administrator, Avicenna spent almost every night with his students composing these and
other works and carrying out general philosophical and scientific discussions related to them.

Avicenna's
Book of Healing
was translated partially into Latin in the 12th century, and the complete
Canon
appeared in the same century. These translations and others spread the thought of Avicenna far and wide in the West. His thought, blended with that of St. Augustine, the Christian philosopher and theologian, was a basic ingredient in the thought of many of the medieval Scholastics, especially in the Franciscan schools. In medicine, the
Canon
became
the
medical authority for several centuries, and Avicenna enjoyed an undisputed place of honour equaled only by the early Greek physicians Hippocrates and Galen. In the East his dominating influence in medicine, philosophy, and theology has lasted over the ages and is still alive within the circles of Islamic thought.

(b.
c
. 1220, Ilchester, Somerset, or Bisley, Gloucester?, Eng.—d. 1292, Oxford?)

R
oger Bacon, who was also known as Doctor Mirabilis (Latin for “Wonderful Teacher”), was an English Franciscan philosopher and educational reformer, as well as a major medieval proponent of experimental science. Bacon studied mathematics, astronomy, optics, alchemy, and languages. He was the first European to describe in detail the process of making gunpowder, and he proposed flying machines and motorized ships and carriages. Bacon (as he himself complacently remarked) displayed a prodigious energy and zeal in the pursuit of experimental science; indeed, his studies were talked about everywhere and eventually won him a place in popular literature as a kind of wonder worker. Bacon therefore represents a historically precocious expression of the empirical spirit of
experimental science, even though his actual practice of it seems to have been exaggerated.

In the earlier part of his career, Bacon lectured in the faculty of arts at the University of Paris on Aristotelian and pseudo-Aristotelian treatises, displaying no indication of his later preoccupation with science. However, beginning in about 1247, Bacon expended much time and energy and huge sums of money in experimental research, in acquiring “secret” books, in the construction of instruments and of tables, in the training of assistants, and in seeking the friendship of savants—activities that marked a definite departure from the usual routine of the faculty of arts. From 1247 to 1257, he devoted himself wholeheartedly to the cultivation of new branches of learning, including languages, optics, and alchemy, and to further studies in astronomy and mathematics. Bacon extolled experimentation so ardently that he has often been viewed as a harbinger of modern science more than 300 years before it came to bloom. However, Bacon's originality lay not so much in any positive contribution to the sum of knowledge but rather in his insistence on fruitful lines of research and methods of experimental study.

Bacon's studies on the nature of light and on the rainbow are especially noteworthy, and he seems to have planned and interpreted these experiments carefully. But his many other “experiments” seem never to have been actually performed; they were merely described. He suggested, for example, that a balloon of thin copper sheet be made and filled with “liquid fire”; he felt that it would float in the air as many light objects do in water. He seriously studied the problem of flying in a machine with flapping wings. Bacon also elucidated the principles of reflection,
refraction, and spherical aberration and proposed mechanically propelled ships and carriages. He used a camera obscura, which projects an image through a pinhole, to observe eclipses of the Sun.

By 1257, Bacon had entered into the Order of Friars Minor, a branch of the Franciscan Christian religious order. However, he soon fell ill and felt (as he wrote) forgotten by everyone and all but buried. Furthermore, his feverish activity, his amazing credulity, his superstition, and his vocal contempt for those not sharing his interests displeased his superiors in the order and brought him under severe discipline. He appealed to Pope Clement IV, arguing that a more accurate experimental knowledge of nature would be of great value in confirming the Christian faith. Bacon felt that his proposals would be of great importance for the welfare of the church and of the universities.

The pope desired to become more fully informed of these projects. In obedience to the pope's command, Bacon set to work and in a remarkably short time had dispatched the
Opus majus
(“Great Work”), the
Opus minus
(“Lesser Work”), and the
Opus tertium
(“Third Work”). He had to do this secretly, and even when the irregularity of his conduct attracted the attention of his superiors and the terrible weapons of spiritual coercion were brought to bear upon him, he was deterred from explaining his position by the papal command of secrecy. Under the circumstances, his achievement was truly astounding. The
Opus majus
was an effort to persuade the pope of the urgent necessity and broad utility of the reforms that he proposed. But the death of Clement in 1268 extinguished Bacon's dreams of gaining for the sciences their rightful place in the curriculum of university studies.

Sometime between 1277 and 1279, Bacon was condemned to prison by his fellow Franciscans because of certain “suspected novelties” in his teaching. The condemnation was probably issued in part because of his excessive credulity in alchemy and astrology. How long he was imprisoned is unknown.

(b. April 15, 1452, Anchiano, near Vinci, Republic of Florence [now in Italy]—d. May 2, 1519, Cloux [now Clos-Lucé], France)

L
eonardo da Vinci was an Italian painter, draftsman, sculptor, architect, and engineer. His genius, perhaps more than that of any other figure, epitomized the Renaissance humanist ideal. His
Last Supper
(1495–98) and
Mona Lisa
(
c
. 1503–06) are among the most widely popular and influential paintings of the Renaissance. His notebooks reveal a spirit of scientific inquiry and a mechanical inventiveness that were centuries ahead of their time.

The unique fame that Leonardo enjoyed in his lifetime and that, filtered by historical criticism, has remained undimmed to the present day rests largely on his unlimited desire for knowledge, which guided all his thinking and behaviour. An artist by disposition and endowment, he considered his eyes to be his main avenue to knowledge; to Leonardo, sight was man's highest sense because it alone conveyed the facts of experience immediately, correctly, and with certainty. Hence, every phenomenon perceived became an object of knowledge.
Saper vedere
(“knowing how to see”) became the great theme of his studies. He applied his creativity to every realm in which graphic representation is used: He was a painter, sculptor, architect, and engineer. But he went even beyond that. He used his superb intellect, unusual powers of observation, and mastery of the art of drawing to study nature itself, a
line of inquiry that allowed his dual pursuits of art and science to flourish.