The Energy of Life: - Guy Brown

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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

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