A man of far-ranging interests and great contrasts: that, in a nutshell, describes Joseph Leidy. A lifelong Philadelphian, he earned his medical degree from Penn’s School of Medicine in 1844 and later served as dean of the school from 1877 to 1888. He was raised only a few blocks from the former site of the University of Pennsylvania’s medical school, then on Ninth Street. And although he became a physician, Leidy practiced very briefly and soon found himself drawn to other related pursuits. Some aspects of the man:
As a medical student, he enrolled in a course in human anatomical dissection run by Dr. James McClintock at his private School of Anatomy, near 10th and Chestnut streets. But the experience was traumatic for the young physician-to-be: he was so revolted by his first human dissection that he fled from the building and did not return for six weeks. Yet he became inured to the process and eventually served as chair of the Department of Anatomy for 38 years!
Leonard Warren, MD, PhD, emeritus professor of Cell and Developmental Biology at Penn’s School of Medicine, notes in his engaging biography of Leidy that his reluctance to practice medicine went even beyond his initial training. At the urging of his father, Leidy rented a house with an office. “The story is told that when he saw his first prospective patient open the gate, he panicked, locked the front door, and retired to an inner room.” Not the best start for a future member of the medical professoriate.
One of the historians of Penn’s medical school, George W. Corner, notes that when Leidy was appointed professor of anatomy, he was only 30 years old, “already recognized at home and in Europe as the country’s foremost comparative anatomist.” He was also the person who most persuasively demonstrated the value of microscopes for medicine and health. As late as the 1850s, many in the medical community continued to be skeptical of the microscope, and Leidy’s work did much to show how much there was to be gained.
Leidy studied both the very, very small and the very large. For 25 years, he was almost the only parasitologist publishing in the United Stated, but he also pursued paleontology and was involved in formally describing and assembling the first dinosaur to be discovered in America, Hadrosaurus Foulkii (1858). Leidy’s monograph Cretaceous Reptiles of the United States, which described the dinosaur more completely and with illustrations, was written in 1860 but not published until 1865, after the Civil War. Despite what other experts believed, Leidy reconstructed Hadrosaurus as a biped and not a quadruped. Hadrosaurus was put on display at the Philadelphia Academy of Natural Sciences, the first ever mounted dinosaur skeleton in the country.
At the other extreme, Leidy’s discovery that had the greatest impact on public health was in the realm of parasites. When he found a minute worm in a cyst in the thigh of his breakfast ham, he did the most natural thing for him: he proceeded to examine it with his microscope. He found it to be Trichina spiralis, the cause of the dangerous trichinosis. On the other hand, although he published his findings on T. spiralis in a local scientific journal, the Proceedings of the Academy of Natural Sciences of Philadelphia, he also did practically nothing to establish the primacy of his discovery when the scientists and journals in Europe failed to give him credit. When Leidy’s friends urged him to claim credit, he declined, stating: “The important thing is that the discovery or fact should be known. It is of little consequence who made it.” Needless to say, such a view is rare in science and medicine -- and, for that matter, life. Still, in 1853 and again later, Leidy wrote that thoroughly heating the pork would kill the parasite. In addition, as Cooper and Ledger report in Innovation and Tradition at the University of Pennsylvania School of Medicine: “Early on, Leidy also investigated flies as transmitters of disease at a time when cleanliness was only beginning to seem important in medicine.”
Although it might seem that Leidy lived sheltered from the real world, such a view would be unfair. Like some other members of Penn’s medical faculty, he served as a military surgeon at Saterlee General Hospital during the Civil War.
And he was not afraid to offer controversial opinions, especially for the time in which he lived. With his vast knowledge of nature, he presented a paper that considered the origins of life. “An attentive study of geology proves that there was a time when no living bodies existed on the earth. . . . Living bodies did not live on earth prior to their indispensable conditions of action, but wherever these have been brought into operation, the former originated. . . . Probably every species has a definite course to run in consequence of a general law, an origin, and increase, a decline, and an extinction.” Leidy’s publication appeared six years before Darwin’s Origin of Species. It was not surprising, as Corner notes, that he was called “infidel” and “atheist” by some people who did not take kindly to his free-ranging study.
The title of Warren’s book on Leidy is The Last Man Who Knew Everything, published in 1998 by Yale University Press. It hardly seems like an exaggeration!