Jointed threads: Joseph Leidy was the first to describe symbiotic bacteria growing together in long strings in animal intestines. Microbiological analyses now link the bacteria with anthrax

Natural History, June, 2005 by Lynn Margulis

Anthrax, once upon a time, was a marginal disease in people, afflicting sheepshearers and few others. Most people who contracted it at all got the cutaneous form of the disease, which forms black scabs on the skin that look like anthracite coal (hence the name "anthrax"). But in autumn 2001, around the time of the terrorist attacks on New York and Washington, deadly anthrax spores began to be spread in letters mailed to news organizations and prominent government officials. Several people inhaled the spores and died from the much more deadly pulmonary form of the disease. Fear of the anthrax contagion was rampant. The very idea that small quantities of white powder in envelopes could be anthrax spores has changed Post office practices to such a degree that they have adversely affected many citizens' daily routines, including my own.

Anthrax spores became infamous as a potential weapon during the Second World War, when the British test-fired anthrax bombs on the Scottish island of Gruinard. The bacterium's infectious spores spread across the island's 520 acres and left Gruinard uninhabitable for nearly fifty years. Not until the late 1980s was the island decontaminated. The cleanup required four years of effort by a large crew; wielding almost 300 tons of formaldehyde--a sobering testament to the durability, both temporal and chemical, of anthrax spores.

What is still unknown, even after the island's cleanup, is the bacterium's ecology. Is anthrax just a kind of bacterial sit-and-wait predator, which bides its time until a sheepshearer cuts himself or a letter handler inhales a cloud of spore-laden dust? The anthrax bacterium is readily grown in laboratory culture. But where is it in nature?

Our eclectic reading habits have helped my students and me disentangle one strand of the anthrax story. We recently discovered that a common laboratory bacterium, identical in all but the most trifling ways with the organism that causes anthrax, lives deep inside the intestines of many healthy animals. But the scientific story of anthrax does not begin with our work, or with the terrorist attacks of 2001, or even with the episode on Gruinard. It begins in the field, on the ties of railroad tracks in the part of New Jersey that borders Pennsylvania, in middle of the nineteenth century. The central figure of the story is a Philadelphia naturalist named Joseph Leidy, once famous but now largely forgotten. Leidy was the first to observe our laboratory bacterium in its natural habitat, living in the intestines of animals.

Leidy's scientific legacy affects everyone, yet he enjoys almost no posthumous reputation. A nineteenth-century polymath, who was initially trained as a physician, Leidy became one of his era's greatest naturalists. He identified the nematode in undercooked pork that is responsible for trichinosis, a debilitating and sometimes deadly muscle disease. He described and named some 400 new species of North American animals, plants, and mushrooms and other fungi. He was the father of modern vertebrate paleontology in North America. He properly interpreted certain fossil remains found in the West as belonging to dinosaurs. Leidy worked tirelessly on the reconstruction of the history of the Earth's surface by investigating metamorphic rocks and eroded minerals. He even discovered a thriving diversity of microscopic life adhering to fish scales, after he had admonished his fishmonger in the Philadelphia open market to neither damage nor remove them.

Exceedingly broad in his choices of nature's gifts to investigate, Leidy published some 400 scientific papers during a fifty-year career. All the papers are single-authored--not because he was uncooperative (there is much evidence of his generosity toward his scientific colleagues as well as his students), but because he was consistently ahead of his colleagues. As Leonard Warren makes clear in his recent biography, Joseph Leidy: The Last Man Who Knew Everything, the main reason the history of science overlooks his accomplishments relates to the breadth of his interests. Leidy's science could never be assigned to a single discipline. Yet his writings never generalize. Leidy stays so close to his own data that to those today who are looking to the past for overarching theories or general principles, he seems to deal only with trivia.

Today's neglect, however, contrasts sharply with the fame he achieved during his lifetime as a scientist, particularly in his native Philadelphia. A larger-than-life statue of him stands outside the city's Academy of Natural Sciences, and the building housing the biology department at the University of Pennsylvania bears his name. Several mountains in the western United States are also named for him. And he helped President Lincoln found the National Academy of Sciences.

In spite of Leidy's wide-ranging interests and activities, he was never away from his first scientific passion for long: the study of the microcosm. Warren conveys Leidy's boundless curiosity for the microworld by quoting a characteristic remark: "How can life be tiresome," Leidy asked, "so long as there is still a new rhizopod [amoeba] undescribed?" Leidy certainly never tired. The archives of the Academy of Natural Sciences in Philadelphia hold the delicate, accurate, even lovingly rendered drawings of the microcosm that he made throughout his career.