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Biophysics, discipline concerned with the application of the principles and methods of must be considered among the most ancient objects of biophysical exploration, because the emission of light by living organisms has long stimulated the curiosity of natural philosophers. Perhaps the first scientific investigation of animal luminescence was that of and in the Principia (1687) wrote of “a certain most subtle spirit which pervades and lies hid in all gross bodies,” and that “all sensation is excited, and the members of animal bodies move at the command of the will, namely, by the vibrations of this spirit, mutually propagated along the solid filaments of the nerves, from the outward organs of sense to the brain, and from the brain into the muscles.” Man’s fascination with animal electricity is illustrated in a letter written by , a physician in Bologna, made the crucial experiment that helped end this controversy. Galvani supposedly was performing experiments with a machine in the company of friends, when, by chance, one member of the party idly probed with a knife the nerves of the thigh of a skinned frog to be used for soup. As the muscles of the frog leg suddenly and unexpectedly contracted, Galvani’s wife noted that a spark had been produced by the electrical machine and “fancied that there was an agreement in point of time.” Although Galvani’s own account of the occurrence differed somewhat in detail from the preceding, it is certain that the experiment was repeated and verified, setting the stage for a long controversy between the advocates of Galvani’s view that current generated by an animal can cause contraction and those of sensitive enough to measure the minute currents generated in muscles and the small potential differences across nerve membranes. Galvanometers were built by the great German 19th-century electrophysiologist gradients and , who became professor of experimental physics at the College of Navarre. The wrote in 1828, “it appears from these new studies that the endosmotic and exosmotic phenomena, which I discovered, belong to a new class of physical phenomena, whose powerful intervention in the vital phenomenon is no longer doubtful.” Following the first quantitative measurements by the botanist , who in 1856 published what is probably the first biophysics text, Die medizinische Physik (“Medical Physics”). Fick developed the laws of diffusion not from experiment but by analogy with the laws governing the flow of , a subject that began to develop with the emergence of the Zeitschrift für Physikalische Chemie in 1887, a journal founded by Dutch chemist . The first volume contains contributions from the most noted physical chemists of the time, including van’t Hoff, Ostwald, Franois Raoult, and Svante Arrhenius. They were concerned with reactions in solution, a central topic in biology because the interior milieu of all living cells is aqueous, and the chemical reactions that sustain life take place in water. The scientific interests of van’t Hoff in particular transcended the boundaries between disciplines. He stressed the importance of the laws of osmosis, which he had clearly delineated, to the economy of all living processes.

Biophysics matured in the 20th century. British biophysicist A.V. Hill described the modern biophysicist in these terms:

Biological phenomena, like many others, show aspects and relations susceptible of physical analysis and interpretation. It is by the choice of problems and by the intellectual processes with which they are formulated and attacked, more than by the particular techniques employed, that a subject can be most clearly defined. There are people to whom physical intuitions come naturally, who can state a problem in physical terms, who can recognize physical relations when they turn up, who can express results in physical terms. These intellectual qualities, more than any special facility with physical instruments and methods, are essential to the make-up of a biophysicist. Equally essential, however, are the corresponding qualities, intuitions, and experience of the biologist. A physicist who cannot develop the biological approach, who has no curiosity about vital processes and functions, who is not willing to spend time in learning the habits of and chemistry; those with physiology, through neurophysiology and sensory physiology. and other large molecules. The laws governing the diffraction of X rays were discovered by the two Braggs, Sir William and was studying the use of X-ray diffraction for the determination of the structure of large biological molecules. He had already used X rays to define the size and shape of the tobacco mosaic virus and showed it to have a regular internal structure. At the Cavendish Laboratory the group that formed around Bernal, a man of wide public and scientific interests, included the Nobel Prize winners , who in 1937 began to use X rays to analyze two proteins fundamental to life, myoglobin and hemoglobin, both of which function in the transport of gases in the blood. Twenty-two years passed before the structures of these proteins were established; the significance of the work is that it provided the basis for an understanding of the mechanism of the action of enzymes and other proteins, an active and fruitful subject of modern investigation.

Interest in biophysics at the Cavendish Laboratory resulted in another important discovery, the structure of deoxyribonucleic acid (DNA), the genetic material. This achievement by a British biophysicist, , was based on X-ray data obtained by , a physicist who had for some years been studying the , especially in studies involving the conduction of nerve impulses. One important scientific product of World War II—the development of vastly improved electronics—largely resulted from radar devices that had been used primarily for locating aircraft. Another product, the atomic bomb, was constructed by way of nuclear reactors that could, in peace time, provide an abundant supply of radioactive isotopes, which are now of great value not only in biophysical research but also in , who showed how the flow of sodium and potassium across the membranes of nerves can be coupled to produce the action potential, a brief electrical event that initiates the action potential, which propagates the nervous signal.

A model of the nerve axon proposed by Hodgkin and Huxley grew from a 19th-century confluence of ideas. made possible an understanding, at the cellular level, of the way in which ions and water are pumped into and out of living cells in order to regulate the ionic composition and water balance in cells, organs, and organisms. The molecular mechanism by which these processes occur, however, remains to be discovered.

In addition to the function of transport, membranes also are utilized as templates on which such molecules as enzymes, which must function in a sequential fashion, can be kept in the requisite order. Although great progress has been made in understanding the mechanisms by which specific atoms are assembled into large biological molecules, the principles involved in the assembly of molecules into membranes, which are organized structures of a higher degree of complexity than large molecules, are not yet very well understood. There is reason to believe that the incorporation of a molecule into a membrane endows it with properties that differ from those of a molecule in solution. A primary task of biophysics is to understand the physical character of these cooperative interactions that are essential to life.

behavioral repertory be predictably related to the behaviour of the elements that compose it.

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