THE INFLUENCE OF EARLY SCHOLARS

Knowledge of anatomy, physiology, and pathology as we now know it began to emerge with the ancient Greeks. They were the first to recognize the distinction between internal and external causes of illness.

To Hippocrates and his followers, we owe the founda­tions of the clinical principles and the ethics that grew into modern medical science. Hippocrates (460-377 BC) was a blend of scientist and artist. He believed that disease oc­curred when the four humors—blood from the heart, yellow bile from the liver, black bile from the spleen, and phlegm from the brain—became out of balance. These humors were said to govern character as well as health, producing phleg­matic, sanguine, choleric, and melancholic personalities. This belief paralleled the even older Chinese tradition, which was founded on the complementary principles of yin (female principle) and yang (male), whose correct propor­tions were essential for health. Hippocrates is identified with an approach to health that dictated plenty of healthy exer­cise, rest in illness, and a moderate, sober diet.

Hippocrates: A blend of scientist and scholar. (Courtesy of the National Library of Medicine)

anatomy, laid the foundations for the later scrutiny of the human body. For Aristotle, the heart was the most im­portant organ. He believed it to be the center of the blood system as well as the center of the emotions. However, Aristotle's main contributions were made to science in general.

The person who took the next major step was Galen (ad 129-199), a physician to the emperors and gladiators of ancient Rome. Galen expanded on the Hippocratic doc­trines and introduced experimentation into the study of healing. His work came to be regarded as the encyclopedia of anatomy and physiology. He demoted the heart—in his view, the liver was primary for venous blood, whereas the seat of all thought was the brain. He described the arteries and veins and even revealed the working of the nervous sys­tem by severing a pig's spinal cord at different points and demonstrating that corresponding parts of the body be­came paralyzed. According to Galen, the body carried three kinds of blood that contained spirits charged by various organs: the veins carried "natural spirit" from the liver; the arteries, "vital spirit" from the lungs; the nerves, "an­imal spirit" from the brain. The heart merely warmed the blood. After Galen's death, however, anatomic research ceased, and his work was considered infallible for almost 1400 years.

As the great medical schools of universities reformed the teaching of anatomy in the early 1500s and integrated it into medical studies, it became apparent to anatomists that Galen's data—taken from dogs, pigs, and apes—often were riddled with error. It was only with the work of Andreas Vesalius (1514-1564) that Galen's ideas truly were challenged.

Vesalius, professor of anatomy and surgery at Padua, Italy, dedicated a lifetime to the study of the human body. Vesalius carried out some unprecedentedly scrupulous dis­sections and used the latest in artistic techniques and print­ing for the more than 200 woodcuts in his De Humani Corporis Fabrica ("On the Fabric [Structure] of the Human Body"). He showed not only what bodily parts looked like but also how they worked. The book, published in 1543, set a new standard for the understanding of human anatomy. With this work, Vesalius became a leading figure in the re­volt against Galen's teachings.

One of the most historically significant discoveries was made by William Harvey (1578-1657), an English physician and physiologist. He established that the blood circulates in a closed system impelled mechanically by a "pumplike" heart. He also measured the amount of blood in the circulatory system in any given unit of time—one of the first applications of quantitative methods in biol­ogy. Harvey's work, published in On the Motion of the Heart and Blood in Animals (1628), provided a foundation of phys­iologic principles that led to an understanding of blood pressure and set the stage for innovative techniques such as cardiac catheterization.

With the refinement of the microscope by the Dutch lens maker Anton van Leeuwenhoek (1632-1723), the stage was set for the era of cellular biology. Another early user of the microscope, English scientist Robert Hooke (1635-1703), published his Micrographia in 1665 in which

William Harvey's most eminent patient, King Charles I, and the future King Charles II look on as Harvey displays a dissected deer heart. (Courtesy of the National Library of Medicine)

he formally described the plant cells in cork and presented his theories of light and combustion and his studies of in­sect anatomy. His book presented the great potential of the microscope for biologic investigation. In it, he inaugurated the modern biologic usage of the word cell. A century later, German-born botanist Mathias Schleiden (1804-1881) and physiologist Theodor Schwann (1810-1882) observed that animal tissues also were composed of cells.

Although Harvey contributed greatly to the under­standing of anatomy and physiology, he was not interested in the chemistry of life. It was not until French chemist Antoine Lavoisier (1743-1794), who was schooled as a lawyer but devoted to scientific pursuits, overturned 100-year-old theories of chemistry and established the basis of modern chemistry that new paths to examine body pro­cesses, such as metabolism, opened up. His restructured chemistry also gave scientists, including Louis Pasteur, the tools to develop organic chemistry.

In 1796, Edward Jenner (1749-1823) conducted the first vaccination by injecting the fluid from a dairymaid's cowpox lesion into a young boy's arm. The vaccination by this English country doctor successfully protected the child from smallpox. Jenner's discovery led to the devel­opment of vaccines to prevent many other diseases as well. Jenner's classic experiment was the first officially recorded vaccination.