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No greater opportunity, responsibility, or obligation can fall to the lot of a human being than to become a physician. In the care of the suffering, [the physician] needs technical skill, scientific knowledge, and human understanding. Tact, sympathy, and understanding are expected of the physician, for the patient is no mere collection of symptoms, signs, disordered functions, damaged organs, and disturbed emotions. [The patient] is human, fearful, and hopeful, seeking relief, help, and reassurance.

Harrison’s Principles of Internal Medicine, 1950

The practice of medicine has changed in significant ways since the first edition of this book was published in 1950. The advent of molecular genetics, sophisticated new imaging techniques, robotics, and advances in bioinformatics and information technology have contributed to an explosion of scientific information that has changed fundamentally the way physicians define, diagnose, treat, and attempt to prevent disease. This growth of scientific knowledge continues to evolve at an accelerated pace.

The widespread use of electronic medical records and the Internet have altered the way physicians and other health care providers access and exchange information as a routine part of medical education and practice (Fig. 1-1). As today’s physicians strive to integrate an ever-expanding body of scientific knowledge into everyday practice, it is critically important to remember two key principles: first, the ultimate goal of medicine is to prevent disease and, when it occurs, to diagnose it early and provide effective treatment; and second, despite 70 years of scientific advances since the first edition of this text, a trusting relationship between physician and patient still lies at the heart of effective patient care.


The Doctor by Luke Fildes depicts the caring relationship between this Victorian physician and a very ill child. Painted in 1891, the painting reflects the death of the painter’s young son from typhoid fever and was intended to reflect the compassionate care provided by the physician even when his tools were not able to influence the course of disease. (Source: History and Art Collection/Alamy Stock Photo.)


Deductive reasoning and applied technology form the foundation for the approach and solution to many clinical problems. Extraordinary advances in biochemistry, cell biology, immunology, and genomics, coupled with newly developed imaging techniques, provide a window into the most remote recesses of the body and allow access to the innermost parts of the cell. Revelations about the nature of genes and single cells have opened a portal for formulating a new molecular basis for the physiology of systems. Researchers are deciphering the complex mechanisms by which genes are regulated, and increasingly, physicians are learning how subtle changes in many different genes, acting in an integrative contextual way, can affect the function of cells and organisms. Clinicians have developed a new ...

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