The Energy of Life:

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.’

But if all the animals of the world are continually consuming large amounts of oxygen, why doesn’t the oxygen in the atmosphere run out, as it does in the jar? Priestley discovered that plants produced large amounts of oxygen when a light was shone on them, and went on to suggest that all the oxygen used by the animals of the world is produced by plants. This suggestion is more or less correct, although the photosynthetic bacteria and algae of the sea (also now classified as plants) contribute as well to the production of oxygen, and it would take over two thousand years for the atmospheric oxygen to run out if all plants stopped producing oxygen. So both the food we eat and the oxygen we breathe come ultimately from plants; this means all energy is derived from plants, who in turn get their energy from the sun.

But if animal respiration was a type of combustion, where within the animal did it occur? Lavoisier and Laplace believed it happened in the lungs. They thought that carbon (and hydrogen) derived from food was brought to the lungs by the blood, and was burnt there with the breathed-in oxygen to produce the waste products of carbon dioxide (and water) then breathed out; and heat, which was absorbed by the blood and distributed to the rest of the body. Their belief that respiration was the combustion of food using oxygen was correct, but they were wrong in thinking that this combustion occurred in the lungs. Their view prevailed for fifty years, although Lagrange, the famous French mathematician, argued that the combustion could not occur solely in the lungs because if all the heat were released there they would be burnt to a cinder. He postulated that oxygen was taken up by the blood and the combustion of food occurred within the blood. This theory was very influential and competed with that of Lavoisier and Laplace. But in 1850, it was found that a frog muscle, separated from the body, still takes up oxygen liberating carbon dioxide; subsequently it was shown that the liver, kidneys, brain and all the body’s other tissues do the same. In the 1870s, the role of blood was demonstrated to be solely the transport of oxygen from the lungs to the tissues, where respiration occurred within the cells, the blood then carrying back the carbon dioxide generated to the lungs. The colour change of blood, from blue-back to red on passing through the lungs, was due to a single component of blood, haemoglobin, which picked up oxygen. Haemoglobin carried oxygen in the blood: it picked up oxygen in the lungs (changing from blue to red), then carried it to the tissues, where it released the oxygen (changing back from red to blue). Thus respiration (or combustion) was occurring not in the lungs but all over the body.

But it was still not clear what relations, if any, respiration and its associated heat production had to life and its processes such as movement, work and thinking. Lavoisier and Séguin, a co-worker, had shown (using Séguin as the experimental subject) that respiration increased during work, after a meal, in the cold, and in deep thought. Thus, there appeared to be a relation between respiration and physiological work, but it was hard to imagine how oxygen consumption or heat production could cause the movement of an arm, let alone the thinking of great thoughts. To bridge that conceptual gap required the imagining of something entirely new, and that something was ‘energy’.

THE VITAL FORCE

The collapse of the four elements theory opened up a cornucopia of matter. If ‘air’ was a mixture of different gases, ‘water’ was a combination of hydrogen and oxygen and ‘fire’ was not an element at all, then what on earth was ‘earth’? The science of chemistry, newly constituted and emboldened at the start of the nineteenth century, was salivating at the prospect of dividing ‘earth’ into thousands of different ‘species’. The concept of species and family had been successfully used by Linnaeus in the eighteenth century to bring order to biological taxonomy, but what were the building blocks of matter and how were they to be classified?

The theory of the elements was recast by Lavoisier, so that there were at least thirty different elements (now known to be about a hundred), existing as elementary, indivisible ‘atoms’ (proposed by Dalton in 1808) and combined in fixed ratios to form more or less stable ‘molecules’. Chemists divided their task between the analysis of inorganic and organic (or ‘organized’) matter, the latter being the constituents or products of living organisms. The alchemists had treated organic matter as if it were a single substance or a small number of elements, for example they had treated distillates of egg or urine as single substances. The chemists set about analysing the many components of egg and urine, using new methods of organic analysis. Lavoisier had pioneered such analysis by burning organic compounds in jars of oxygen and collecting the carbon as carbon dioxide and hydrogen as water. By quantifying the amount of carbon (C), hydrogen (H), and oxygen (O), a formula of the compound could now be written down; starch was, for example, thought to be C12H10O10. This formula was mistaken, and arose from the misconception that water was HO rather than H2O. But these methods were rapidly improved and applied with great enthusiasm by several German chemists, in particular Liebig and Wöhler. In 1835, Wöhler wrote: ‘Organic chemistry appears to me like a primeval forest of the tropics, full of the most remarkable things’. These first optimistic biological chemists did not, however, comprehend the full complexity and extent of their new field. It is now thought that there may be roughly five million different organic compounds in the human body and these compounds may be organized in an almost infinite number of different ways.

Nineteenth-century Germany, although not yet united, had become the major centre for scientific and technological innovation. Perhaps partly in reaction to the rise of science and industrialism, the Romantic movement developed in late-eighteenth-century Germany producing a scientific philosophy known as Naturphilosophie. This bizarre hybrid of Romantic philosophy and science contributed to a resurgence of interest in the vital force and the relationships between all forces.

Justus von Liebig (1803–1873) dominated German chemistry and biochemistry in the nineteenth century, sometimes to the detriment of biology. The son of a dealer in drugs, dyes, oils, and chemicals, von Liebig gained an interest in chemistry assisting his father. But he did badly at school and was derided when he suggested a career as a chemist. He learned to make explosives from a travelling entertainer, terminating an apprenticeship in pharmacy when he accidentally blew up the shop. His father packed him off to university to study chemistry but he was soon arrested and sent home after becoming too involved in student politics. Somehow he eventually earned his doctorate and went to work in Paris with one of the best French chemists of the time, Joseph Gay-Lussac. In the 1820s he took a position at a small German university at Giessen, and over the next twenty-five years produced a veritable mountain of chemical data.

However, von Liebig did not produce this data himself, rather he invented the research group as a quasi-industrial means of producing scientific results. Taking over an unused barracks as a chemical laboratory, he staffed it with junior scientists as lieutenants, students as foot soldiers and with himself as the distant but all-powerful general. This model of the research group was so successful in producing the large volumes of research required in the industrial world that it was widely adopted and remains the main means of producing scientific research today. This is in strong contrast to the pre-industrial system of the individual scientist thinking up experiments and carrying them out himself, with or without assistance. Von Liebig was both arrogant and argumentative and had a number of angry disputes with other scientists. His success gave him considerable power, through his control over scientific journals, appointments, and societies. The parallels with science today are unavoidable. It is dominated by a relatively small number of politicians of science who control the boards of scientific societies, journals, conferences, grant-giving bodies, and appointment boards. Success in a scientific career still depends to a certain degree on gaining the patronage of these politician-scientists.

Von Liebig started the prodigious task of analysing the millions of different combinations of elements – molecules – that make up a human being. Some kind of order was brought to this chaos by distinguishing three main types of molecule: carbohydrates, fats, and proteins. At first it was thought that these ‘organic’ molecules could only be produced by living organisms, using some kind of vital force. But in 1828 Friedrich Wöhler, a friend and colleague of von Liebig, found that he could chemically synthesize urea (an important component of urine) without any living processes being involved. Ultimately, this would lead to the melting of the boundary between the living and the non-living, but not yet.

Although von Liebig showed that living organisms were constructed from a large number of organic chemicals, he believed that a ‘vital force’ was required to prevent these complex chemicals from spontaneously breaking down. He came to this conclusion because, in the absence of life, they did tend to break down, either by oxidation (combination with oxygen as in burning), putrefaction (as in flesh after death), or fermentation (conversion of sugar to alcohol). Von Liebig’s concept of vital force was similar to that of a physical force such as gravity or the electric force, but was only present in living organisms. Within the living body, this vital force opposed the action of the chemical forces (causing oxidation, putrefaction and fermentation), thus preventing the decay of the body so evident after death. Von Liebig also claimed that the vital force caused muscle contraction because he thought there could be no other way to account for the control of muscle by mind. When a muscle contracted, some of the vital force was used up to power the contraction. Consequently, immediately after the contraction, there was less vital force to oppose the decay (oxidation) of chemicals in the muscle, which therefore speeded up with an associated increase in respiration. The vital force acted as a brake on the chemical forces and when it was consumed by muscle contraction, the chemical forces speeded up. This is akin to the famous story of Peter, the little Dutch boy, sticking his finger in the leaking dam, trying to prevent the sea washing away the fields and town (just as the vital force prevented the chemical forces from eroding the body). This erroneous interpretation was used to explain Lavoisier and Séguin’s important discovery that respiration (the process of consuming oxygen to produce carbon dioxide and heat) greatly increased when a human or animal was working or exercising. Although von Liebig’s conception of the vital force was a form of vitalism, in the tradition of Aristotle, Paracelsus, and Stahl, the concept was more mechanistic in its appeal to Newtonian forces and foreshadows the concept of energy, formulated in the mid-nineteenth century.

Von Liebig’s belief that everything could be explained by chemistry and the vital force was opposed by Theodor Schwann (1810–1882). This clash proved catastrophic for the sensitive and as yet unestablished Schwann. Schwann’s productive work lasted just four years (1834– 1838), while he was still only in his twenties, but it was enough to spark a reorganization of biology almost as fundamental as that of Lavoisier’s of chemistry. Schwann’s first venture was to isolate a muscle from a frog and measure the force produced by the contracting muscle when it was held at different lengths or pulled against different weights. He found the muscle contracted with the greatest force when it was at the length that it was naturally found in the body. These experiments were seen as sensational in Germany, because for the very first time a vital process supposedly mediated by a vital force was treated and quantified in the same way as an ordinary physical force. It was now possible to give a physical account of vital processes, or reduce them to physical forces. This approach, however, did not please von Liebig and other champions of the vital force. Indeed Mayer later used Schwann’s experiment specifically to disprove von Liebig’s account of muscle contraction.

Schwann’s next achievement was the isolation of an enzyme which he called pepsin from the digestive juices. An enzyme is a biological substance present in small quantities which promotes a chemical reaction without being itself converted by the reaction. But ‘enzyme’ is a twentieth-century notion, in the nineteenth century they were known as ‘ferments’. For the alchemists, a ferment was a small quantity of active substance which when added to a passive substance could transform it into an active one similar to the ferment. For example, fire was the ferment converting flammable substances into flame and the philosopher’s stone was the ferment transmuting base metals into gold. Fermentation is the process responsible for the leavening of dough producing bread and for converting grapes into alcohol, making wine. This apparently magical transformation had been recognized since antiquity, but how exactly this happened was unclear, although it was known to require a ferment – yeast. Having discovered a ferment in digestive juice, Schwann concluded that digestion was a kind of fermentation. Von Liebig and the other chemists considered digestion, on the other hand, as a purely chemical process due to the action of acids on food. So when Schwann published his findings in von Liebig’s journal, von Liebig added a rather sceptical note to his paper.

Schwann then turned his attention to the nature of fermentation itself: one of the central scientific and technological problems of the nineteenth century. Von Liebig and the chemists believed fermentation was purely chemical and did not involve any biological organisms or processes. Schwann and two other researchers independently discovered that fermentation was a biological process caused by a fungus – yeast – the cells of which could be viewed through a microscope and could be destroyed by boiling. Schwann also showed that the putrefaction of meat was biologically mediated too, it could be slowed by heating and sealing the meat. These biological breakthroughs incensed the chemists who soon got their revenge. In the meantime, Schwann embarked on a microscopic study of the role of cells in animal development and in biology generally. The resulting ‘cell theory’ published in 1839 revolutionized how the body was viewed.