SUMMARY OF EVENT
The development of human physiology as a science required an accurate anatomical understanding of the human body. Scholars, physicians, and artists gained anatomical knowledge through the dissection of cadavers, a practice that began in Europe in the fourteenth century and gradually gained recognition in the fifteenth and especially the sixteenth century. Scientific developments of the seventeenth century led scientists to regard humans as machines, and this mechanical approach dominated research at that time. Albrecht von Haller, a former student of the Dutch mechanist Herman Boerhaave, coined the term anatomia animata, or living anatomy.
Boerhaave viewed the human being as a machine composed of hollow and solid elements. Influenced by the teachings of Boerhaave, Haller furthered physiologic understanding by carrying out numerous animal experiments. His areas of interest were multiple: He studied the development of chicken embryos and adopted the preformationist standpoint that the ovum contains a miniature being—a homunculus (little human)—that starts to grow once activated by semen. His work in the field of pulmonology demonstrated that lung expansion requires an airless pleural space. His research correctly ascribed digestive properties to saliva and pancreatic juices, and his understanding of the process of hearing approached that of modern science.
Haller designed hundreds of animal experiments to study muscle and nerve action. Denuded anatomical areas were exposed to thermal, chemical, or mechanical injury. The different reactions of the animal to the noxious stimuli allowed Haller to differentiate between “irritable” and “sensible” tissues. Muscles exhibited “irritability,” a contraction of muscle fibers upon stimulation, whereas nerves displayed “sensibility” and were responsible for pain perception. The term “irritability” had been used a century earlier by British physician Francis Glisson, who presumed that all tissues could contract. Haller, however, showed through careful experimentation that irritability was restricted to muscle fibers.
Albrecht von Haller. Portrait by Johann Rudolf Huber, 1736.
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Image via Wikimedia Commons. [Public domain.]
Having observed that compression of the spinal cord and specific brain areas interfered with the transmission of nerve impulses, Haller could only speculate on the mode of communication between nerve and muscle. He discarded the possibilities of electrical conduction and vibration, hypothesizing that “juice” flowing from the central nervous system through the peripheral nerves led to muscle contraction. The concepts of irritability and sensibility, which Haller first announced in 1739, were discussed again in his monograph De Partibus Corporis Humani Sensibilibus et Irritabilibus (1753; A Dissertation on the Sensible and Irritable Parts of Animals, 1755). The full development of Haller’s concept of nerve and muscle function was published in Elementa Physiologiae Corporis Humani (1757-66; Elements of Human Physiology).
During his lifetime, Haller published three textbooks of physiology, including a heavily annotated edition of professor Boerhaave’s lectures, a text entitled Primae lineae physiologiae (1747; Dr. Albert Haller’s Physiology, 1754), and the multivolume set Elementa Physiologiae Corporis Humani, in which he systematically presents the complete anatomic and physiologic knowledge of the human body. Elementa Physiologiae Corporis Humani not only contained macro- and microanatomical information on organ systems but also encompassed their physical and chemical properties. Haller discussed each organ structure and the experiments leading to understanding specific organ functions in minute detail. He provided references for the theories and experiments cited and credited scientists who had contributed to the data.
Haller critically analyzed the available information and avoided drawing unfounded conclusions. In addition to offering a critical analysis of the existing body of knowledge about human physiology, he discussed those contexts in which insufficient or inconclusive data were available to draw firm or meaningful conclusions. His text, therefore, stood as a complete, well-researched scientific work of experimental physiology, detailing the entire state of the field as it then existed and emphasizing what now is the golden rule of medical science: Knowledge and understanding of the human body must be based on valid, well-conceived experiments and reflect the efforts of each contributing researcher.
Haller, who had conducted most of his experimental work during the seventeen years he taught as a professor of anatomy, botany, and surgery at the University of Göttingen, began writing Elementa Physiologiae Corporis Humani upon his return to Switzerland in 1753. The first volume, Fibra, Vasa, Circuitus Sanguinus (Fibers, Vessels, The Circulation of Blood), was published in 1757. He completed the work in 1766, when the eighth volume, Fetus hominisque vita (The Human Fetus and the Life of Man), came out in print. Like the first volume, the second volume, Sanguis, Ejus Motus, Humorum Separatio (1760; Blood, Its Motion, and the Separation of Fluids), was dedicated to Frederick V of Denmark.
In the preface to volume 5, Sensus Externi Interni (1763; External and Internal Senses), Haller defended his theory of irritability and sensibility. The third volume (1761) treated respiratory function and voice, and volume 4, which appeared in 1762, discussed the brain, nerves, and muscles. Volume 6, Deglutitio, Ventriculus, Omenta, Lien, Pancreas, Hepar (Swallowing, Stomach, Omenta, Spleen, Pancreas, Liver), and volume 7, Intestina, Chylus, Urina, Semen, Muliebra (Intestine, Juice, Urine, Seminal fluid, Female Organs), were published in 1764 and 1765, respectively.
A complete German translation of Haller’s monumental work appeared between 1759 and 1776. Portions of the work have also been translated into French and Dutch but very little into English. In 1774, the first eight pages of Fibra, Vasa, Circuitus Sanguinus were translated into English and published in The Medical Magazine, Or, General Repository of Practical Physic and Surgery under the title Elements of Physiology. Other translations were published in subsequent numbers.
Haller’s support of preformationism may have delayed progress in understanding embryology. Still, his breakthrough work in neurology spurred scientists to explore how the transmission of nervous impulses occurred. Luigi Galvani and Alessandro Volta, drawing inspiration from Haller, later demonstrated that muscles would contract when electrically stimulated and paved the way for the development of electrophysiology.
SIGNIFICANCE
Albrecht von Haller’s contributions to modern physiology facilitated the understanding of pathologic processes and ultimately led to progress in the treatment and prevention of disease. A mechanistic understanding of life evolved from the simplistic view of bodies as compositions of “beams and levers” and “pipes and vessels” to Haller’s realization that living tissues are characterized by their specific functions: The intrinsic property of muscle is to contract, and that of nerves is to feel.
The discovery that the reaction to a stimulus depended on the tissue’s organizational makeup—that is, the discovery that tissue was specialized or programmed to act a certain way—was entirely new. Haller’s perception that tissues possess “vital properties” stimulated scientific thinking, leading to the concepts of an “internal milieu” and “body homeostasis.” In the nineteenth century, it led to the further discovery that even nerves were specialized, as the same stimulus applied to different nerves could produce sight, smell, touch, taste, or sound.
It became increasingly apparent that the harmonious functioning of living organisms required an intricate messenger system: The role of the binding of hormones to their receptors in initiating the informational cascade between different organs has been elucidated, as well as the role of three-dimensional protein structures, play in cellular functioning.