The Energy of Life:

Hippocrates (c. 460–377 BC) is called the founding father of medicine, and his theories of disease, cure and physiology influenced medicine and biology up until the eighteenth century. However, his own life is so mythologized that it is impossible to distinguish the basic events of his life, or even whether he really ever existed. According to legend, Hippocrates was a physician from Cos, and he practised medicine in Thrace, Thessaly and Macedonia, before returning to Cos to found a school of medicine. This school flourished from the late fifth century to the early fourth century BC, producing a vast number of highly original medical texts. Copies of around seventy of these books survive. These were conventionally attributed to Hippocrates, although he probably wrote none of them himself. The defining characteristic of Hippocratic medicine was its rejection of religious and philosophical explanations of disease, and its search for an empirical and rational basis for treatment.

Since prehistoric times, disease had been thought caused largely by gods, evil spirits, or black magic. A cure could thus be effected by ejecting the sin, spirit, or magic from the sufferer via various processes of purification. In Greece, traditional medicine was practised by priest-physicians in temples dedicated to the god Asclepius. In these temples of health, disease was apparently diagnosed partly on the basis of dreams and divination, and partly on the symptoms. Cures were half rituals and spells, and half based on fasting, food, drugs and exercise. According to later legend, Hippocrates was descended from the god Asclepius and brought up on Cos as son of a renowned priest-physician. The relationship between secular medicine (represented by Hippocrates) and religious medicine (based on faith healing or magic) in ancient Greece is difficult to discern, although apparently not as antagonistic as today.

Hippocrates and his followers accepted the doctrine of the four elements as an explanation for the natural world, but their concern as doctors was with disease’s causes and treatment. The four elements – earth, fire, air, and water – cannot be seen in anything approaching a pure form in or on the body. Also they knew relatively little about the inside of the body, because dissection was prohibited on both religious and ethical grounds. So the Hippocratics concerned themselves with what they could see and use in the diagnosis of disease, particularly the bodily fluids: blood, saliva, phlegm, sweat, pus, vomit, sperm, faeces and urine. Gradually the doctrine evolved that there were only four basic fluids (humours): blood, phlegm, yellow bile, and black bile. Blood can appear in cuts, menstrual flow, vomit, urine or stools. Phlegm is the viscous fluid in the mouth (saliva) and respiratory passages and comes out through the mouth and nose in coughs and colds. Yellow bile is the ordinary bile secreted by the liver into the gut to aid digestion; it is a yellow-brown fluid that colours faeces. The identity of black bile is not entirely clear, perhaps originally referring to dark blood clots, resulting from internal bleeding, which may appear in vomit, urine or faeces. However, the four humours did not only refer to these particular fluids, but were thought to be the body’s basic constituents. Health was thought to be due to the balance of these humours, and ill health an imbalance of the humours. Epilepsy was, for example, thought to be caused by an excess of phlegm in the brain blocking the flow of pneuma (vital spirits) to the brain. Thus treatment sought to restore the balance between the humours by removing the humour that was present in excess, for example by bloodletting, purging, laxatives, sweating, vomiting, diet or exercise.

The four humours (blood, phlegm, yellow bile, and black bile) were associated with the four elements (air, water, fire and earth), the four primary qualities (hot, cold, dry and wet), the four winds, and the four seasons. A predominance of one humour or the other gave rise to four psychological types. Thus, the ‘sanguine’ type, resulting from a dominance of blood, was cheerful and confident. ‘Phlegmatic’ types (with too much phlegm) were calm and unemotional. ‘Choleric’ or ‘bilious’ people (with too much yellow bile) were excitable and easily angered. ‘Melancholic’ types (too much black bile) were, obviously, melancholy, that is sad or depressed, with low levels of energy. This was the earliest psychological classification of character or temperament, and was used to categorize different people right up until modern times. No obviously superior way of classifying temperament has, in fact, yet been devised. The theory of the four humours dominated medical thinking until about three hundred years ago. Many patients were still being bled even in the nineteenth century.

The Hippocratics and Greeks generally believed in positive health – health could be improved much further than the absence of illness towards well-being. Modern medicine is mainly concerned with negative health (i.e. illness), and how to restore us to health, rather than with helping us feel ‘on top of the world’. The Hippocratics were much concerned with regimen or lifestyle, both in health and disease, mainly involving the correct balance of food and exercise. The importance of exercise to both physical and mental health was recognized, and was institutionalized in gymnasia where exercise was practised on a social basis. If you had gone to Hippocrates in 400 BC (assuming you could find him) complaining of lack of energy he might have given you a detailed regimen involving an exercise programme, with a warning about too much or the wrong type of exercise; a diet, particularly including strained broths; a lot of hot and/or cold baths, and massages; some sex (if lucky); and some obscure advice about the relations between your energy and the wind direction, season of the year, etc. This would have been, in general, a reasonably effective regimen, and you would be lucky to get better advice today from your doctor.

Aristotle (384–322 BC) was a colossus of thought, straddling the end of classical Greece and Renaissance Europe. He dominated the world of the intellect, sometimes as a benign sage and other times as malevolent dictator. His thoughts were worshipped to such an extent that they circumscribed any attempts at original thought, until their eventual rejection by Renaissance Europe, when he was blamed for stifling two thousand years of thought. Much of Aristotle’s influence derives from his having been a pupil of Plato (possibly the greatest thinker ever), and then tutor to Alexander the Great (possibly the most successful conqueror of all time).

Aristotle’s views of the physiology and energies of life were derived mostly from Empedocles, Hippocrates and Plato. Nutrition, vital heat and pneuma (vital spirit) were pivotal to this view. The heart was central to the body, the origin of consciousness and the instrument of the soul, and the source of heat, pneuma, blood, and movement for the rest of the body. Pneuma was an air-like substance or spirit, containing vital heat, which was always in rapid motion, and as such was a source of both heat and motion inside the body. Pneuma was derived from air, and brought through the mouth, nose and skin to the heart, where it supplied the vital heat. A steady flow of nutrient fluid from the gut supplied the heart, and the heating of the fluid within the heart produced blood. The blood and pneuma were then distributed through vessels to the rest of the body, where the blood coagulated to form the tissues of the body under the influence of the ‘nutritive soul’. There was no circulation of blood, rather the blood was produced in the heart (and liver and spleen) and then distributed to the tissues, with no return flow. Many vessels (the arteries) were thought to be hollow (as indeed many are if the blood escapes from them after death), and were, thus, thought to carry air or pneuma through the body. The brain cooled the blood, and functioned to prevent the blood from overheating. The muscles were simply a protective layer, keeping the rest of the body warm, and had no function in movement. Nerves, as such, were unknown, as most are difficult to see; but large nerves and tendons were collectively called neura and were thought to function in movement of the limbs, by acting as cords pulling the bones. The pneuma supplied the ‘go’, energy or movement throughout the body.

Aristotle’s pneuma was also the motivating force outside the body – in the physical world. According to his mechanics, the natural state of things was rest rather than movement; so that the continuous movement of an object such as an arrow in flight required pneuma to be continuously pushing the arrow from behind. Thus we can see that pneuma was energy for Aristotle, although of course it had a rather different role in classical thinking. Aristotle was also partly responsible for the theory of the four qualities: hot, cold, wet, and dry, which were components of the four elements. Thus earth was cold and dry, water cold and wet, air hot and wet, and fire hot and dry. This became a very important doctrine in later medicine and alchemy, because it gave a key as to how to alter the ratio of the elements; thus, for example, water could be converted to air by heating, or air could be converted to fire by drying.

Aristotle was the first authority to use the term energeia, from which we derive the word ‘energy’. But he used it to mean the ‘actual’, as opposed to the ‘potential’, as he had an obscure theory that ‘change’ involved turning from a potential thing into an actual thing. So when something happens, a potential happening changes into an actual happening. Thus for Aristotle energeia was tied up with change and activity, but in what seems now a rather obscure and abstract way.

Although Aristotle’s view of physiology and energetics was most influential, it was far less original and interesting than that of Plato. Plato was not really interested in physiology, as he had his mind set on higher things, but he wanted to find a physical location for the various parts of the soul that he had identified. For, according to Plato, the body is peopled by a bickering community of souls, ruled over by a somewhat prissy head. The immortal soul is in the head, and the mortal soul located from the neck down. The courageous part of the mortal soul is found above the diaphragm, where it can both listen to reason (from the head) and subdue the lower regions. This soul’s main home is the heart; when the head thinks that the passions are out of control it informs the other organs, and the heart starts leaping with excitement and overheating. The lungs can then save the day by cooling and providing a cushion for the overtaxed heart. Below the diaphragm dwells the ‘appetitive’ soul, which while necessary for life needs to be kept chained, far from the seat of reason. This part of the soul is controlled by the liver, capable of listening to reason. The liver regulates the nether regions either by contracting to block passages causing pain and nausea, or by spreading cheerfulness and serenity to the surrounding parts of the soul. The length of the gut is intended to prevent food passing through too quickly, which would cause an insatiable appetite, and make mankind impervious to culture and philosophy. The spinal marrow is called the universal ‘seed-stuff’ (also the source of semen) fastening the soul to the body. The different kinds of soul are found in various parts of the marrow, while reason and intellect occupy the brain. This community-of-souls theory of the body shows how appealing, but empty, intentional explanations of physiology can be. In order to progress, the supernatural had to be replaced by mechanical causes and energy as the source of change.

The deaths of Aristotle and Alexander in 322 and 323 BC respectively marked the end of classical Greece. But Alexander had spread Greek culture across the known world, ushering in the age of Hellenism, which was a fusion of Greek and Persian culture. Hellenism’s most successful centre was in Alexandria, briefly flourishing under Ptolemy I. A former pupil of Aristotle, Ptolemy attracted some of the greatest Greek scientists and thinkers to Alexandria’s Museum and Library. Two brilliant physicians, Herophilus and Erasistratus, were able for the first time to practise dissection of the human body there and used this to great effect. This had been impossible previously due to the commonly held assumption that the body retained some sensitivity or residual life after death. Changing beliefs about the soul’s relation to the body enabled Herophilus and Erasistratus to dissect dead humans, and even, it has been claimed, live criminals. The result caused a revolution in anatomy: the exploration of a whole new realm below the human skin. The nerves, and their relation to the brain and muscles, were discovered. The brain was explored and the fluid-filled cavities within (ventricles) were thought to be filled with a new form of pneuma: psychical pneuma (animal spirits). This psychical or mind pneuma radiated out from the brain, through the nerves, to energize the muscles. However, Alexandrian scientific creativity gradually declined and the influence of eastern mysticism increased.

In the second and first centuries BC, Rome swept the political stage while largely adopting Greek culture and thinking. Into this new world was born Galen (AD c. 129–216), antiquity’s last great physician and biologist. An architect’s son from Pergamon, he studied philosophy then went to Alexandria to learn dissection. Returning to Pergamon, he became surgeon to a school of gladiators, where he gained invaluable experience in treating wounds. In AD 169 Galen was summoned to Rome to become personal physician to Marcus Aurelius, the Philosopher Emperor. These duties do not seem to have been too onerous as Galen continued his writing and scientific work, in the end producing over 130 books. Many are commentaries on and syntheses of previous medical knowledge, including textbooks and treatises on almost all diseases, treatments and methods of diagnosis. These books became the central texts of medicine for fifteen hundred years. Galen was seen as a kind of medical theologian, for whom anatomy was both praise and veneration of the one true God. And this, twinned with his interpretation of the body in Aristotelian terms, guaranteed the acceptance of his writings by later Christian and Islamic authorities.

Galen’s doctrine of pneuma synthesizes earlier ideas of the Hippocratics, Aristotle, the Alexandrians and Stoicism (a philosophy founded by Zeno). Pneuma can be translated as ‘airs’, and was thought to be an invisible force within the air. Pneuma was translated into Latin as spiritus, but is most naturally translated today as ‘energy’. To the Stoics, pneuma was a non-material quality or form imposed on matter. Pneuma pervaded the universe and was the vehicle of cosmic ‘sympatheia’, by which each part of the universe was sensitive to events in all others. Pneuma acted as a force field in the air, immediately propagating movement to the edge of the universe and then back again. This is reminiscent of modern concepts of sound waves or of electromagnetic waves moving through the air. Inside the body, pneuma pervaded the blood vessels and nerves and enabled the transmission of sensitivity, movement and energy.

Galen distinguished three different kinds of pneuma inside the body: natural spirit, vital spirit and animal spirit. These were produced by the three main organs and their associated faculties or souls (the idea was derived from Plato). The liver, hub of the appetitive soul and supposed source of the veins, produced natural spirits. The heart, centre of the spirited soul and source of the arteries, produced vital spirits. And the brain, home of the rational soul and source of the nerves, produced animal spirits. The liver took digested food from the stomach and guts, concocting it into dark, venous blood containing natural spirits, which when distributed to the rest of the body was assimilated forming the substance of the organs. This was the basis of the appetitive (or nutritive) faculty of the liver. Taking venous blood, the heart concocted it with pneuma, derived through the lungs from the air, producing red arterial blood, full of vital spirits. These vital spirits, distributed throughout the body by the arteries, were then responsible for all other living processes, apart from those of movement and thought. The brain transformed vital spirits into psychical spirits, which then became responsible for consciousness, and when distributed by the nerves, for muscle movement and sensation.

Pneuma is the closest we get in antiquity to the modern concept of energy. It is a non-material, potential form of motion, action and heat, and its transformations correspond to the transformations of energy. The ghost of pneuma still haunts the modern idea of energy, but has been transmuted into an altogether more pragmatic concept by today’s more materialistic scientists.

After Galen, there was little innovation in Greek and Roman science and an increasing emphasis on mysticism and theology. In the fourth century, the official religion of Rome became Christianity, at that time diametrically opposed to the scientific spirit. In the fifth century, the western half of the Empire was invaded by German tribes, ushering in the Dark Ages, which lasted almost a millennium. The eastern, Greek-speaking side of the Empire lasted much longer, gradually diminishing in power. In the seventh and eighth centuries, the Islamic Arabs conquered Syria, Egypt, North Africa and Spain, absorbing Greek knowledge. Although it was not until the eleventh century and later that Christian Europe was finally able to reabsorb Greek learning from the Arabs, and, at last, to spark the Renaissance.

Alchemy forms a bridge between the ancient Greek and Roman learning and the birth of modern science in seventeenth-century Europe. While the alchemists’ quest started two thousand years ago in Alexandria, China and India, as late as 1680 Isaac Newton still devoted most of his time to the mysterious art. Because it existed through the dark ages of knowledge and science, alchemy reflected the time’s religious, symbolic and mystical forms. But it also kept many of its practitioners in contact with classical knowledge and experimental science. The alchemists appear to modern eyes as a bunch of wacky mystics. It seems incredible that sober citizens came up with this bizarre combination of chemistry and religion. Why not engineering and sex, or poetry and gardening? However, many alchemists were intent on the very practical goals of limitless money and life everlasting. What could be more modern than that? Unfortunately for them, the theories of alchemy were completely wrong.

The importance of alchemy to our story is that it attempted at least to understand what things are made of, and much more importantly how they change. If we look at a stone or egg naïvely, it is hard to see what they consist of and where their potential for change comes from. What is it about an egg that enables it to turn into a chicken? What is it about a piece of wood allowing it to burn? What is it about a lump of gold that makes it last forever? The alchemists put all these questions into the fire. Fire was the great transformer and transmuter: separating metals, distilling essences and cooking food. In many ways the alchemist was a cook, his technology was derived from the kitchen, and he sought to transform his raw materials, through recipes, herbs, and inspiration into perfection. The alchemist also sought to isolate (by distillation and other methods) the essence or spirit of things, as a metal is isolated from ores or alcohol distilled from wines or a drug ‘purified’ from a plant. They thought adding the essence of gold (known later as the ‘philosopher’s stone’) to other metals would turn the base metals into gold. Unfortunately for the alchemists, they did not yet realize that gold was an unchangeable element, more fundamental than earth, fire, air or water and that there was no essence of gold to be given to other metals. The alchemists’ real achievement was that by their slaving over a hot stove and forging mental concepts, they slowly transformed the categories and concepts by which matter was seen, eventually enabling the evolution of chemistry and biochemistry.

What have we learnt from our journey through the scientific progress of the classical world? From Empedocles, Aristotle and the Atomists, we discovered that the world and its changes do not have to be understood in terms of the wishes and desires of gods, spirits or even matter itself. It can rather be explained in terms of the structure and interactions of a small number of basic particles or elements, each too small to see, but that when mixed together make up visible matter. The changes we see are due to forces of attraction or repulsion between these particles, leading to changes in the composition of matter. From Hippocrates and Galen, we learnt that death and disease are not due to the will of gods, devils or sorcerers, but can be explained in terms of the workings and malfunctions of the body machine. And this can be understood in terms of the body’s various solid organs with different functions, the various vital liquids that flow within and between them, and the various invisible spirits or gases that animate the body. However, this knowledge does not explain how someone moves a hand by willing it, how thought is possible, or how life differs from death. Our journey must continue into the modern world in pursuit of the energy of life.

THE ENLIGHTENMENT

Our modern world was sparked into existence by the scientists and thinkers of seventeenth and eighteenth-century Europe. Without their intervention, we could now be living very differently, perhaps in some sort of impoverished, fundamentalist state. But it required revolutions and counter-revolutions, heroes and anti-heroes, blood and tears to achieve the transformation of thought that came to be known as ‘The Enlightenment’.

It was the work of four scientists in particular that prepared the ground for this new scientific approach. Their discoveries exploded the medieval conventions of cosmology. The first scientific bombshell unleashed on an unsuspecting medieval world was the discovery that the earth was not at the centre of the Universe. Copernicus (1473– 1543) wisely did not ever openly state this while alive, but the shockwaves from his heliocentric theory rocked the medieval church nonetheless. Then, Kepler (1571–1630) showed that the planets do not move in circles, but ellipses. Furthermore, Galileo (1564–1642) used a telescope to show that all was not perfect among the ‘heavenly bodies’; the moon was pitted with craters and volcanoes, Jupiter had moons, and the blanket of the Milky Way in fact consisted of millions upon millions of stars. Isaac Newton (1642–1727) then went on to show that the planets were not a law unto themselves, but rather followed the same rules as everything on earth.

Even more fundamentally important, Kepler, Galileo, and Newton stated that everything, ranging from teapots to planets, ‘obeys’ mathematically precise, mechanical ‘laws’, conjuring up a clockwork universe, policed by cold, mechanical ‘forces’. There was no more room for spirits, gods or God. No room even for Empedocles’ forces of love and strife. Things did not move (or even stop moving) because they wanted to do so, but because they were ‘forced’. According to Newton’s (and Galileo’s) first law of motion, movement itself was no longer a sign of life or spirit. Only a change in speed or direction was an active process, and this was due to an external ‘force’. Thus, amazingly, all movement in the world, apart from that of living animals, could be explained as passive and mechanical. The non-living world suddenly became frighteningly cold, empty and dead. In place of spirits, forms and purposes, there were forces. In fact, the ‘forces’ that inhabited Newton’s universe were not so radically different from the preceding ‘spirits’. The new ‘forces’ were unexplained and inexplicable, but had an inanimate mechanical basis, as opposed to the living freedom of ‘spirits’. These forces rigorously obeyed precise, mathematical laws, whereas the spirits had followed their desires. The technological wonder of the age was the mechanical clock; this in turn became a metaphor for the Universe itself. With the invention of the clock, Time itself began to tick, and the whole Universe was forced to beat in time. But it was not only the non-living things that were forced to bow to the new mechanical spirit of the age. René Descartes (1596–1650) proposed that animals were also purely mechanical devices, automata with no feelings or consciousness. The processes of the body could be explained just using mechanical laws. Thus, for example, the nerves acted as pneumatic pipes, transmitting pressure changes of animal spirits (psychical pneuma) at the nerve endings to the brain, and from there through other nerves to the muscles, where the pressure inflated the muscles.

‘Now according as these spirits enter thus into the concavities of the brain, they pass thence into the pores of the substance, and from these pores into the nerves; where according as they enter or even as they tend to enter more or less into the one or the others, they have the power to change the shape of the muscles in which these nerves are inserted, and by this means to make all the limbs move.’

He went on to compare the nervous functions of the body and mind to the automatic puppets, then fashionable, which, driven by hydraulic pipes, could move and even seemingly speak.

Descartes did leave a small bolthole for the soul in the pineal gland, a small almond-shaped organ at the centre of the brain. He suggested the soul was radically different to matter and not subject to the laws of physics, but interacted with the body, through the animal spirits inside the pineal gland. The soul consisted of an unextended, indivisible, thinking substance, constituting the mind, all thoughts, volitions and desires. But all else on earth, including the human body and brain, was a vast clockwork mechanism.

Descartes has been much demonized as the inventor of ‘Dualism’, which purported that the world consists of two radically different substances: mind and matter. Dualism is, however, an ancient concept present in all early cultures; in Classical Greece, it is Plato’s concept of two separate worlds of appearances and perfect ideas, and in Aristotle’s substance and form; it is consistently found throughout Hindu, Jewish, Christian and Islamic thought as the separation of body and soul. Descartes did not invent Dualism. He was, on the contrary, a radical materialist, considering almost everything to consist solely of one substance, matter, but perhaps his nerve failed when it came to a denial of the soul. It is conceivable Descartes might have done this were it not for the Inquisition, which had, in 1616 and 1633, condemned Galileo for his heretical scientific beliefs.

Whether Descartes intended it or not, his and other mechanical philosophies separated body and mind even further, so that they were commonly regarded as radically different. The body and brain was seen as a cold machine and analysed in relation to the latest technical toy, which ranged across clocks, levers, hydraulic puppets, steam engines, electric robots and electronic computers. Whereas the mind became some wishy-washy, non-material thing, too slippery to analyse, and best left to theologians and philosophers to chew over. Consequently the trail to body energy and mind energy splits in two here, only rejoining relatively recently.

One of the world’s greatest philosophers, mathematicians and scientists, Descartes appears to have been intrinsically lazy. Rarely getting up before midday, he worked short hours, and read little. Where did he find the energy for his great works? One answer may lie in his lack of routine. He had no need of a job, as after selling his father’s estates he lived off his investments. So he immersed himself in his studies and whenever boredom threatened he joined an army – trying out those of France, Holland and Bavaria. He was sociable, but when friends distracted him from his conceptual tasks, he moved away. Descartes never married, and his only natural child died at five, so there was never any need to adapt to a domestic routine. He was capable of short bursts of extreme concentration. On a cold morning of the winter of 1619–20 when he was with the Bavarian army, Descartes climbed into a large oven to keep warm. He stayed in there all day thinking, and when he eventually emerged had half completed his critical philosophy, which then became the foundation of modern philosophy. This anecdote stresses the importance of removing all external distractions to intense thought. But Descartes would never have managed this feat without also removing the further internal distractions of routine thoughts, feelings and desires. And, most importantly, he would never have got anywhere without supreme self-confidence. Only powered by optimistic egotism could he reject all previous thinking, rebuilding the conceptual map of the world. Confidence is the sine qua non of creativity. Descartes’ power finally gave out when lured to Sweden by Queen Christina, he was impelled to give her daily lessons at five in the morning. This proved too much for his weak constitution and he was dead within six months.

Although Descartes tried, he didn’t succeed in his application of the new mechanical approach to biology. But, in the hands and mind of William Harvey (1578–1657), this approach yielded a remarkable success with his discovery of the circulation of the blood. Blood had been thought made in the liver and heart, passing directly from the left to right sides of the heart, and then out to the rest of the body, never returning to the heart; although it might ebb and flow in the same vessels. The heart’s beat was thought due partly to breathing and partly to the formation of heat and spirits inside the heart. Thus the heart was not thought to pump the blood. Harvey showed by experiment and quantitative argument that it received as much blood as it pumped out. It was not making blood but circulating it. The heart was not an alchemist, but a mechanical pump. Furthermore, Harvey proved it was a double pump: veins brought blood from the rest of the body to the right side of the heart, which pumped the blood to the lungs; it returned from there to the left side of the heart, then was pumped to the rest of the body, through the arteries. It is telling that the function of the heart and vessels was elucidated by the use of a mechanical analogy, inspired by a pump and pipes for circulating water.

There was one glaring hole in Harvey’s scheme. He could not see how the blood got from the arteries, through the organs and back to the veins. This was because the vessels involved, the capillaries, were too small for Harvey to see. So it was left to Marcello Malpighi (1628–94) to complete our image of the circulation by finding the capillaries using the newly discovered microscope. The microscope opened up a new miniature world to discovery, just as the telescope had laid bare the heavens, and the dissecting knife had opened the body beneath the skin. The first users of the microscope must have experienced the thrill of entering unknown territory. Malpighi described for the first time the structure of the lungs, spleen, kidneys, liver and skin. Many features of the human body still bear his name (such as the Malpighian tubes of the kidney), just as the explorers of sea and land left their names on the Americas. Antoni van Leeuwenhoek (1632–1723), a Dutch draper and pioneer microscopist, discovered striped muscle, sperm, and bacteria. And then it was the English scientist Robert Hooke (1635–1703) who first saw and named ‘cells’, but failed to recognize their significance.

Comprehension of the microscopic structure of living things is essential to any understanding of how they work. In this respect they differ from mechanical machines, which are constructed on a macroscopic level from components that at a microscopic level are both homogenous and uninteresting. By contrast, living things appearing to the naked eye as fairly simple, reveal mindboggling complexity at a microscopic scale. This vertiginous intricacy continues down to the atomic scale. Both the mechanical biologists, and all previous generations of biologists were, of course, completely unaware of this vital piece of knowledge. Some biological functions (such as how the blood circulates) are understandable at the macroscopic level but the most important secrets (such as why the blood circulates) are located on a molecular scale, beyond the reach of even the microscopists. So, mechanical biologists made relatively little progress, despite their occasional breakthroughs with the circulation of the blood and the optics of the eye.

In reaction to the mechanical (and chemical) explanations of life proposed in the seventeenth century, many scientists and thinkers defended life as radically different from the non-living, due to the possession of a ‘vital force’. One such vitalist was Georg Ernst Stahl (1660–1734), who explained life and disease as the actions of a sensitive soul or ‘anima’, inhabiting every part of the organism preventing its decay. This ‘animism’ was an example of ‘vitalism’, the belief that life was not explicable in purely mechanical and chemical terms, harking back to Aristotle and earlier. Stahl was also a chemist, and proposed the infamous phlogiston theory. This theory interpreted combustion, i.e. burning with its accompanying flame and heat, as due to the release of a special substance called phlogiston, a stored heat energy. Stahl believed that plants took phlogiston from the air, and incorporated it into their matter, so if the plant was then burnt (as wood or straw) the phlogiston could escape into the atmosphere again. Or if, alternatively, the plants were eaten by animals, phlogiston could be released by the animal’s respiration, a kind of combustion inside the body. The phantom of phlogiston beguiled chemists for about 100 years until finally extinguished by Lavoisier, who also disproved Stahl’s vitalism. However, Stahl had already died in a state of severe depression long before the demise of his theories.

This historical journey has led us to a cold and abstract world of science, stripped bare of gods and spirits, ruled instead by laws and forces. We have ventured below the skin of appearances, and must travel inwards to ever smaller scales if we are to penetrate the meaning of life. The human body has become a machine, to be taken apart piece by piece. But the next veil of mystery which hides the secret of life is not a physical or mechanical one. The old dream of the alchemists is suddenly to bear fruit in the form of the chemistry of life.

THE REVOLUTION

Human attempts to find the secret to the energy of life had stalled for a thousand years but now were finally beginning to make some progress. This was due to the startling achievements of one man: Antoine Laurent Lavoisier (1743–1794), creator of the Chemical Revolution and victim of the French Revolution. Aristotle, Galen, Paracelsus, Stahl and others had all recognized that there was some relation between breathing, heat and life but the nature of this relation was no longer clear. Harvey had shown that blood circulated from the lungs to the rest of the body and back again, via the heart, but why did it circulate in this way? Was it bringing something to or removing from the tissues? The analogy between life and combustion had been noted, but combustion was seen as a kind of decomposition, so its relevance to life was still unclear.

Several British scientists had shed light on these mysteries. Robert Boyle (1627–1691) discovered an animal could not survive long in a jar after the air was removed by a vacuum pump, suggesting animal life is dependent on air or on some component of air. Boyle’s assistant, Robert Hooke (1635–1703) showed that the mechanical movement of the chest in breathing was inessential to life, since he was able to stop the chest moving in animals while maintaining life by blowing air in and out with bellows. Richard Lower (1631–1691), a pioneer of blood transfusions, showed that the colour change in blood from blue-black in the veins to red in the arteries occurred as it passed through the lungs.

Incredibly, some seventeenth-century scientists believed that life was powered by something akin to gunpowder. The invention of gunpowder in the late middle ages had led to the belief that its components (sulphur and nitre) were also responsible for thunderstorms, volcanoes and earthquakes. This supposition was apparently confirmed by the sulphurous smell of volcanoes and thunderstorms. Lightning was thought to result from a nitre-like component of air, the nitrous spirit. It was proposed that this nitrous spirit was extracted from the air by the breathing body, then combining with sulphurous compounds already contained in the body to produce a combustion – the explosion of life. The gunpowder theory of life is another fascinating example of how technological change provided new analogies and innovative ways of thinking about biology.

Between 1750 and 1775, the main gases were discovered by British chemists: carbon dioxide by Joseph Black in 1757; hydrogen by Henry Cavendish in 1766; nitrogen by Daniel Rutherford in 1772; and oxygen independently by Joseph Priestley in 1774 and the Swedish chemist Karl Scheele in 1772. However, these gases were not considered distinct chemical substances, but rather, types of air, as Empedocles’ four elements theory still held sway – 2,200 years after his death. So, for example, carbon dioxide was known as fixed air, and oxygen as dephlogistonated or fire air. But the scientific stage was set for a revolution: the overthrow of the four elements, the extinction of phlogiston, the rejection of vitalism, and for the creation of chemistry and physiological chemistry.

Lavoisier was an unlikely revolutionary: his father was a lawyer and his family was part of the prosperous French bourgeoisie. He received the best possible education and studied law, gaining an interest in chemistry from a family friend. The French Academy of Sciences had been in existence since 1666, and at only 21, Lavoisier decided he wanted to be a member. He successfully investigated various methods of public street lighting, and was awarded a gold medal by the king and at just 25 was elected to the Academy. He then embarked on the series of chemical experiments that was to reshape the world of science. But, like most other contemporary scientists, he had to finance his own experiments, so he used his maternal inheritance to purchase membership of a tax-collecting firm. While this provided him with financial security, it was to eventually prove fatal, as tax collectors were not popular at all after the French Revolution. His career did, however, also provide him with an introduction to his thirteen-year-old future wife, Marie, the daughter of another tax collector. This turned out to be a wise move, as Marie rapidly became a proficient scientist herself, serving as an able assistant to all Lavoisier’s works.

In 1775 Lavoisier was appointed scientific director of the Royal Gunpowder Administration, and started working on methods of improving the production of gunpowder and on the general nature of combustion, oxygen and respiration. When he finally disproved the phlogiston theory, the Lavoisiers staged a celebration in which Marie dressed as a priestess, burning the writings of Stahl on an altar. But 1789, the year of publication of Lavoisier’s great work Traité élémentaire de chimie, also marked the start of the French Revolution. Although he served in the revolutionary administration, his bourgeois and tax-collecting credentials finally told against him, and he was imprisoned during the Reign of Terror. Marie was given the chance to plead for his life, but chose to energetically denounce the regime instead. Lavoisier was tried and guillotined in 1794.

Lavoisier’s first target was the theory of the four elements. Alchemists had found that boiling water for a long time resulted in the disappearance of water and appearance of a solid residue. They thought this resulted from the transmutation of one element – water – into another – earth – by the action of heat or drying. We now know the solid residue is derived partly from salts dissolved in impure water and partly from the container in which the water is boiled. Lavoisier showed this by boiling purified water in a sealed glass container for one hundred and one days. He found that a small amount of solid matter appeared in the water but by weighing the matter, water and container demonstrated that all this matter was derived only from the container, thus proving water could not be transmuted into earth.

Lavoisier next turned his attention to the burning of metals. Heating metals results in a rusting of the surface, which had been compared to combustion. But according to phlogiston theory (equating phlogiston with the element of fire) combustion results from the release of phlogiston from the material into the air, and should thus result in a decrease in weight of the remaining material. Lavoisier tested this by measuring the weight of the metal before and after heating. He found that the metal always gained weight after heating; and furthermore, part of the air around the metal disappeared after the heating. Thus, the phlogiston theory of metal combustion could not be correct: Lavoisier interpreted his findings to mean that during the heating of the metal, some of the air combined with the metal to form rust, thus increasing the weight of the metal. But what was it in air that combined with the metal?

At this point (October 1774) Joseph Priestley visited Paris, dining with Lavoisier and other French scientists. This crucial meeting was to provide the essential key to Lavoisier’s research, but also resulted in the two scientists’ long-running, bitter dispute over scientific priority and plagiarism. Priestley (1733–1804) was a Presbyterian minister from Yorkshire who developed a surprising bent for science. While investigating the properties of carbon dioxide, derived from the brewery next door, Priestley discovered that when the gas was dissolved in water, it produced a pleasant drink (soda water, present in most soft drinks today). He received a prestigious medal from the Royal Society for this invention and was subsequently recruited by the Earl of Shelburne to be his secretary and resident intellectual. Priestley set up a laboratory at Shelburne’s country estate and proceeded to isolate a number of gases. In August 1774, Priestley first isolated oxygen by collecting the gas resulting from heating mercuric oxide. He found a candle burned more brightly and a mouse survived longer in a jar of this gas than in ordinary air. Priestley considered the new gas to be a variety of air (‘pure air’) and adhering to the phlogiston theory, later named it ‘dephlogisticated air’. At this crucial point Shelburne took Priestley to Paris and at a fateful dinner with Lavoisier, Priestley told of his recent experiments. Whether or not this meeting was the inspiration for Lavoisier’s subsequent experiments was later hotly disputed. But Lavoisier immediately repeated Priestley’s experiment of producing oxygen by heating mercuric oxide, realizing that this new gas must be the substance in air combining with the heated metal to produce rust (metal oxides). But Lavoisier interpreted the new gas as a separate substance (or element), not a variety of air, and later named it ‘Oxygen’ – which is Greek for ‘acid former’, because he believed (wrongly) that all acids contained some oxygen. In April 1775, Lavoisier presented his findings at the French Academy without reference to Priestley, claiming he had independently discovered oxygen. Priestley subsequently disputed his priority in the discovery of oxygen. There now seems little doubt that Priestley and Scheele discovered oxygen, but because they used the phlogiston theory and only had a crude conception of chemical elements, they failed to interpret their findings as a new substance.

Another bitter dispute followed over the composition of water. Water was still regarded as an element, but Priestley, Cavendish and James Watt (famous for his discovery of the steam engine) had found that if a mixture of hydrogen and oxygen (or air containing oxygen) was ignited with a spark, then water was produced. They were, however, slow to publish their findings. An assistant of Cavendish visited Paris in 1783, innocently telling Lavoisier of their findings on the production of water from hydrogen and oxygen. Lavoisier immediately returned to the laboratory repeating the experiment, and went even further by reversing it; he heated steam to produce oxygen and hydrogen. He swiftly published the result, claiming priority for the discovery. This understandably caused a furore. But the important knowledge was that water was not, as previously thought, an element, but a combination of oxygen and ‘hydrogen’ (another name coined by Lavoisier, meaning ‘generator of water’). At last the four elements theory was falling apart and something had to take its place. Lavoisier provided that new system, essentially modern chemistry, according to which there are many elements, including oxygen, hydrogen, nitrogen, carbon and phosphorus, which can combine in various ways to produce compounds, which depending on their nature and conditions may be either solids, liquids, or gases.

Lavoisier’s key contribution here was to accurately measure the change in weight and to use the principle of conservation of mass – the idea that regardless of what you do to an object it will not change in weight (as long as no mass escapes). Before Lavoisier’s breakthroughs it was not clear whether matter could appear or disappear during reaction or transformations. Lavoisier showed by weighing that the mass stayed the same during a reaction, and explicitly stated the principle of Conservation of Matter: matter could not be created or destroyed. He used this principle to track where the matter was going in a whole series of reactions. Because of Lavoisier’s principle, contemporary improvements in weighing techniques contributed to the development of chemistry, as much as the microscope contributed to biology. He also provided a nomenclature for chemicals, still in use today. All these changes amounted to a Scientific Revolution, which transformed alchemy into chemistry. The new system was rapidly adopted throughout Europe, only rejected by a few die-hard phlogiston theorists, including perhaps unsurprisingly, Priestley. There was no love lost between these two great scientists. Priestley, the experimentalist, regarded Lavoisier’s theories as flights of fancy; while Lavoisier, the theoretician, characterized Priestley’s investigations as ‘a fabric woven of experiments hardly interrupted by any reasoning’.

Priestley moved to Birmingham in 1780 and joined the Lunar Society, an influential association of inventors and scientists including James Watt, Matthew Boulton, Josiah Wedgwood (engineer and pottery manufacturer), and Erasmus Darwin (poet, naturalist and grandfather of Charles). In 1791 Priestley’s chapel and house were sacked by a mob angered at his support for the French Revolution. He fled to London, and then, in 1794 at sixty-one, emigrated to America, settling in Pennsylvania, and becoming one of the New World’s first significant scientists.

Lavoisier then teamed up with Pierre-Simon de Laplace, one of the greatest mathematicians in France. They wanted to investigate the relation between combustion and respiration. Combustion is the process of burning, usually accompanied by flame, such as the burning of a candle. Respiration had originally described breathing, but it had been discovered that this process was associated with the consumption of oxygen and production of carbon dioxide; ‘respiration’ thus came to stand for this process of gas exchange by organisms. Both combustion and respiration consumed oxygen from the air, replacing it with carbon dioxide and both produced heat. But could the conversion of oxygen to carbon dioxide by a living animal quantitatively account for all its heat production? In other words, was respiration really combustion, accounting for the heat produced by animals? They decided to compare the heat and carbon dioxide production of a respiring guinea pig and of burning charcoal (pure carbon). Lavoisier and Laplace invented a sensitive device to measure heat production, although it only worked well on days when the temperature was close to freezing. When, at last, everything was working, they found the burning of charcoal and the guinea pig’s respiration produced the same amount of heat for a given amount of carbon dioxide. They concluded therefore that the heat production of animal respiration was due to combustion of carbon (from food) within the animal, and that respiration was in fact slow combustion. From this result they had the audacity to claim that a vital living process was in fact a simple chemical reaction. And they were right – well, partly.

Priestley had again been working on similar lines. He had shown that candles and mice lasted approximately five times longer in a jar of oxygen than in a jar of ordinary air. This is because ordinary air consists of one fifth oxygen and four fifths nitrogen, a gas which does not support life. Priestley said of oxgyen (or rather, as he called it, dephlogisticated air):

‘It is the ingredient in the atmospheric air that enables it to support combustion and animal life. By means of it most intense heat may be produced; and in the purest of it animals may live nearly five times as long as in an equal quantity of atmospheric air. In respiration part of this air, passing the membranes of the lungs, unites with the blood and imparts to it its florid colour, while the remainder, uniting with phlogiston exhaled from venous blood, forms mixed air.’