Animal Heat
While the mechanical philosophy dealt with the problem of motion quite well, and the vitalists with growth and reproduction, the problem of heat generation by animals remained a tough nut to crack. Why was heat so important? Most living things are warm, and when they die they grow cold. Clearly, heat had something to do with life. Already Pythagoras and Democritus considered heat, or more precisely “innate heat,” the key to understanding life. For the ancient Greeks, the problem of heat was (literally) at the heart of the mystery of life. They believed that a kind of fire existed in the heart and that the lungs were needed to cool the heart’s fire and remove exhaust. Plato writes in his Timaeus: “In the interior of every animal the hottest part is that which is around the blood and veins; it is in a manner an internal fountain of fire, which we compare to the network of a creel, being woven all of fire and extended through the centre of the body, while the outer parts are composed of air.” This thinking persisted for centuries—even Harvey still believed that the heart was a source of heat and that the blood circulation he had discovered was a way to distribute heat throughout the body.
Such ideas were based on reasonable inferences from observations: Clearly, the heart resided near the center of the body—which seemed like a good place to put a stove—and it distributed warm, life-giving blood throughout the body. As for how the heart generated this heat, it was understood that heat was generally associated with fire. Thus, it seemed that some kind of “slow fire” in the heart generated the heat of the body. The ancients also guessed correctly that life’s heat must be fueled by food. “[Food] is used up by our heat as oil is by a flame,” Galen observed.
Galen and the ancients knew that both fire and life are extinguished in the absence of air, but they did not know why. Galen lamented: “if we could discover why flames are in these cases [when deprived of air] extinguished, we should perhaps discover what advantage the heat in animals derives through respiration.” This blueprint for further research was not taken seriously by natural philosophers until fifteen hundred years later. In the early sixteenth century, animistic ideas about the nature of innate heat were still rampant. The French physician Jean François Fernel (1497–1558) believed that the innate heat enters the body once the embryo becomes an individual. He seemed to confuse innate heat with the religious idea of a soul. Descartes can be credited with bringing heat back into the realm of science, although his enthusiasm for mechanistic explanations led him astray when he speculated about the role of heat in the heart. While he believed in Harvey’s blood circulation, he also believed the heart’s motion was caused by an expansion of the blood due to the intense heat in the heart, and not by muscular contractions.
The primacy of heat as the central principle of life was challenged by the Belgian physician Jan Baptist van Helmont (1579–1644), who pointed out that frogs are quite cold, but also quite alive. Moreover, animals did not die when heat left them, but the heat left when animals died. Van Helmont was fond of chemical explanations, in the tradition of Paracelsus, and therefore saw heat as the result of chemical processes in the body, not the cause of such processes. He broke with the ancients, who had believed in heat as being innate, that is, inherent to living beings, like a soul. Van Helmont saw heat as a phenomenon that could be explained, as long as the right causes were identified.
The first experiments designed to answer Galen’s question were performed by Robert Boyle (1627–1691), John Mayow (1641–1679), and Robert Hooke—English mechanical philosophers and fellows of the still young Royal Society of London. They established that something in the air was involved in both fire and respiration. In both cases, heat was generated. Thus, the air drawn through the lungs did not cool the heat in the heart, but rather was an ingredient to produce heat in the first place. The mechanical philosophers speculated about “nitrous spirits” in the air, which would combine with sulfurous compounds in the blood in some kind of fermentation, generating the heat. Their science was still mingled with alchemy, and more sophisticated experiments were needed to solve the mystery.
The lack of a sound chemical explanation for innate heat allowed the pendulum to swing back to mechanical explanations in the eighteenth century. La Mettrie’s teacher, the Dutch physician Herman Boerhaave (1668–1738), believed that the heat of the body was generated by friction when the blood was forced through the arteries. Many other physicians and scientists, thoroughly steeped in the mechanical philosophy of the time, shared this idea. However, these mechanical views were heavily criticized by the vitalists. An Edinburgh physician, John Stevenson, wrote in his 1747 paper “Cause of Animal Heat”: “Not content with the ingenious . . . application of levers, ropes and pulleys to the bones, muscles and tendons; . . . millstones were brought into the stomach, flint and steel into the blood vessels, hammer and vice into the lungs. But all to no good purpose; there being certain bounds beyond which mechanical principles and demonstrations do not reach.” The friction theory of animal heat was disproved by experiments, including an experiment by Benjamin Franklin in 1769. Franklin showed that fluids running through blood vessels could never generate enough heat. He resorted to chemical explanations and, observing that fermenting fruit had almost the same temperature as a living being, resurrected the fermentation theory of Hooke and Boyle.
Progress had to await a better understanding of the origin and nature of heat, just as Galen had predicted fifteen hundred years earlier. Because air seemed to be central to heat and respiration, natural philosophers tried to understand the chemical effect of air on various processes, from life to the oxidation of metals (or “calcination,” as they called it, not knowing of oxygen). Confusingly, heat and fire sometimes released different kinds of “air” and changed the nature of the substance being heated or burned. Was this air “fixed” inside the substances and released upon burning? How did the air get to be trapped inside a solid? As long as air was still considered an element, it was difficult to understand why different airs disappeared in some reactions, while others emerged.
The mystery of fire seemed solved when the German (al)chemists Johann Joachim Becher (1635–1682) and Georg Ernst Stahl (1659–1734) developed the phlogiston theory of fire. According to this theory, phlogiston was a substance that was released upon burning, respiration, and calcinations, and this release generated heat. This theory was widely accepted until well into the eighteenth century. However, problems with this theory quickly emerged: For example, when a metal was heated in air, it turned into its “calx” (oxide). Phlogiston theory predicted that the calx would be lighter than the metal, because the calx formed when the phlogiston was released from the metal. But experiments showed the opposite to be the case: The calx was heavier than the metal. The proponents of the phlogiston theory explained this curious fact by claiming the phlogiston had levity, that is, some kind of antigravity. Such desperate explanations invited ridicule from the anti-phlogiston faction. The leader of this faction was the French chemist Antoine Lavoisier (1743–1794), who together with his wife and fellow chemist, Marie-Ann Pierrette Paulze (1758–1836), vanquished the phlogiston theory.
Lavoisier was a French nobleman who made a living collecting taxes (a job that landed him on the guillotine in 1794) and who, “on the side,” revolutionized chemistry. It is little exaggeration to call Lavoisier the Newton of chemistry. The first person to clearly recognize the different chemical natures of the various airs, he discovered that water, earth, and air were compounds or mixtures. These discoveries thus eliminated most of the elements of the ancients—elements that were still taken seriously in the eighteenth century. The only element remaining after Lavoisier’s overhaul of chemistry was fire or heat (which he renamed “caloric”). The demise of this last element was not far behind: At the dawn of the nineteenth century, Benjamin Thompson showed that heat is a form of energy (more about this in Chapter 3).
Lavoisier’s most important experiment on animal heat consisted of measuring the heat output of a guinea pig versus t
hat of burning coal, in relation to the carbon dioxide (“acide crayeux”) generated during respiration or combustion. This was a tricky experiment: To measure the heat output, he used an ice calorimeter, invented jointly by him and Pierre-Simon Laplace (1749–1827). The instrument consisted of an isolated bucket with hollow walls stuffed with ice. Heat was measured by the amount of ice melted by whatever process was taking place inside the box. To avoid melting by the surrounding air, these experiments were done in the winter, when the temperature was just barely above freezing. The output of carbon dioxide was measured by placing the coal or the animal into a bell jar, so the air could be collected and analyzed. Lavoisier found that breathing and combustion generated roughly the same amount of heat for the same amount of carbon dioxide released. Respiration was now proven to be “slow fire.” Not knowing about cells, Lavoisier placed this fire in the lungs.
While Lavoisier did not discover where and how heat was generated, he ushered in the age of quantitative physiology and established the connection between biology and thermodynamics. These findings, and his development of a rational chemistry based on true chemical elements, their compounds and mixtures, earns him a place among the greatest scientists of all time. When the French revolutionaries condemned him to death in 1794, the presiding judge declared: “The Republic needs neither scientists nor chemists; the course of justice cannot be delayed.” The mathematician Joseph Louis Lagrange saw it differently: “It took them only an instant to cut off his head, but France may not produce another such head in a century.”
This gruesome end to the life of a scientific genius can serve as a warning to all who see no value in supporting science. With Lavoisier’s death, Germany and England quickly overtook France in the sciences (and in industry).
Mechanism Fails
Dissatisfaction with scholasticism, with blind adherence to Greek philosophy, and with mysticism of all kinds gave rise to the mechanical philosophy. As champions of rational thought and experimental evidence, the mechanical philosophers revolutionized science and philosophy. In physics, chemistry, and astronomy, they marched from triumph to triumph.
By the late eighteenth century, however, the limitations of the mechanical approach were starting to show. The mechanical picture of life, while informed by observations and experiments, turned out to be bloodless and impotent. The functions of the body, the interactions of organisms, the development of life, and the life of the mind did not yield to purely mechanical analogies. The specter of purpose was difficult to exorcise. The “purpose” of an acorn was to make an oak; the “purpose” of a brain was to think. How did the acorn know that it should become a tree? How could a lump of gray matter think? Could a clockwork explain such mysteries?
This state of affairs led to a schizophrenic approach to life: On one hand, a mechanistic approach had undeniably yielded important insights into how life worked; on the other hand, this approach seemed insufficient to account for what made matter alive. The basic attribute of life, its self-sustaining, self-organizing activity, remained outside the grasp of purely mechanistic explanations. Out of this tension, modern biology arose.
Germany and other central European countries, as well as Russia, became the center of biological research in the nineteenth century. The word biology was coined during this time. The German biologists developed sophisticated methods to study the development of embryos and the function of organs and muscles. The Germans improved microscopy and sample preparation techniques and studied the functions of the sense organs. In these studies, they accepted a mechanical picture of life’s processes to a point, but were very aware that living organisms were not at all like a clock or a steam engine. There had to be something else.
Embryology, in particular, was a problem for the mechanists. Studying the development of a chick or a tadpole in detail, biologists saw matter take form, and a complex living being emerge from a lump of cells in a mysterious unfolding. You could not explain such a miraculous process with levers, pumps, and randomly moving atoms. It was absurd. Clearly, organic structures served a purpose. Living organisms had to be fundamentally different from anything encountered in the inanimate world.
The vexing problem of embryology expressed itself in the debates between the preformationists and the epigenesists. These debates revealed some surprising fault lines between the mechanists and the vitalists. Preformation was the idea that every living being had to be preformed in the egg or sperm. If you were a preformationist, you had to believe that before little Annie was born, there already existed a tiny version of Annie in the germ cells of her parents, too small to be detected by a microscope. Once activated by her father’s sperm, the tiny embryo started to grow in her mother’s womb, thus there was no necessity of unformed matter to acquire form, as the form was already present in the ovum of the mother. Surprisingly, preformationism was often the favored position of the mechanists, who we may naively consider the more scientific of the two camps. Yet, preformation seemed nonsensical: Taken to its logical conclusion, all of humanity, all those billions of humans who ever lived, had to already exist in Eve’s ovaries as tiny versions of themselves.
Epigenesis, by contrast, claimed that unformed matter was shaped into a complex living being during embryonic development. This also posed problems. What directed this development? How could a lump of undifferentiated matter turn into a chicken or a frog? Mechanism could not explain how such spontaneous self-organization would work, even in principle. Epigenesis was the favorite of the vitalists. The formation of biological complexity from unformed matter was a task equal only to their beloved vital force—indeed, it was proof that such a force had to exist.
The dissatisfaction with mechanism led to a more romantic philosophy of life. Proponents of Naturphilosophie (“nature philosophy”) saw a vital force acting throughout nature, striving to bring about higher and higher forms of being—a notion that sounded very much like animism. However, many German biologists were averse to explanations that seemed to invoke supernatural forces. While they allowed that a vital force was necessary, this vital force needed to be a part of nature and subject to scientific inquiry.
Trying to steer a path between mechanism and vitalism, the German philosopher Immanuel Kant (1724–1804) and his friend, biologist Johann Friedrich Blumenbach (1752–1840), created a new approach to the study of life: teleomechanism.* In 1790, Kant wrote to Blumenbach: “Your recent unification of the two principles, namely the physico-mechanical and the teleological, which everyone had otherwise thought to be incompatible, has a very close relation to the ideas that currently occupy me.” In the Aristotelian tradition, Kant and Blumenbach thought that life was directed by purpose (Greek teleo). In particular, Blumenbach espoused the existence of a formational drive (Bildungstrieb in German), which would provide the “means [by] which [the organisms] receive a determinate shape originally, then maintain it, and when it is destroyed repair it where possible.” Blumenbach, and the biologists who came after him, did not see this vital force as a separate entity from the organism. Rather, it was a force contained within an organism, a result of its special organization and structure.
This view of self-contained special forces in organically organized bodies helped shape biology into an autonomous science. With the renewed recognition that life was special, life scientists could develop their own methods, ideas, and approaches. The role of the biologist was to find the rules by which special vital forces acted on organic matter. The German biologist Carl Friedrich Kielmeyer (1765–1844) went as far as to create a set of Newtonian laws that the vital forces would obey. First, he identified the forces acting in living beings: sensibility, irritability, reproduction, secretion, and propulsion. Then, he came up with various laws for these forces (most of which were subsequently proven wrong) and called them “the physics of the animal realm.”
The biological tradition founded by Kant and Blumenbach led to several important discoveries in embryology and physiology. One of the most profound discoveries wa
s the cell theory—the recognition that all living beings were made of smallest units, called cells. This insight was long overdue—after all, Hooke had coined the term cells, for the little compartments he saw in cork, as early as the late 1600s. The cell theory is usually credited to Matthias Jakob Schleiden (1804–1881), a German botanist; Theodor Schwann (1810–1882), a German zoologist; and Rudolf Virchow (1821–1902), a German physician, although numerous other scientists, from several countries, contributed to the final theory.
The cell theory corresponded to a kind of biological atomism, with cells as the “atoms” of life. But cells were not indivisible like atoms. Microscopists discovered even smaller structures inside cells, starting with the cell nucleus, which was named by Robert Brown in 1833.
The age of the German vitalist biologists opened up new vistas for inquiry. The teleomechanists were superb experimentalists and founded new schools of embryology, developmental biology, botany, and physiology. If these scientists were misguided in their theoretical ideas about vital forces, we may forgive them: Their experimental results have generally withstood the test of time.
An Irritable Frankenstein
With an anxiety that almost amounted to agony, I collected the instruments of life around me, that I might infuse a spark of being into the lifeless thing that lay at my feet. It was already one in the morning; the rain pattered dismally against the panes, and my candle was nearly burnt out, when, by the glimmer of the half-extinguished light, I saw the dull yellow eye of the creature open; it breathed hard, and a convulsive motion agitated its limbs.
Life's Ratchet: How Molecular Machines Extract Order from Chaos Page 4
