* * *

Rubber as it naturally occurs is a mess. In hot weather, it melts. In cold, it cracks and shatters. It was almost useless to people until 1845, when chemists invented a way to make natural rubber into tires, called vulcanization.

In the ensuing years, a fierce competition to perfect the process erupted. The initial solution involved a mix of heating the natural rubber and adding sulfur. The product was pliable but durable, able to withstand most any weather. Vulcanization could be done in massive factories, like that of Goodyear. Shortly after, the British chemist Alexander Parkes figured out a way to forego the intensive heating and produce a superior rubber. Cold vulcanization instead used a solvent to treat the natural rubber: carbon disulfide.

It’s impossible to say how many people today have benefited from this discovery—billions of users of rubber products, from shoe soles to hoses to tires—while a lower but not insignificant number suffer because of it.

“Carbon disulfide is a very unique toxin—in its manifestations, truly protean,” the physician Paul Blanc told me. “And some of them are quite startling, most especially its capacity to cause insanity. But also atherosclerosis in the heart and the brain, as well as Parkinsonism.”

The CDC adds to that list birth defects and menstrual disturbances. But before you panic and starts discarding your tires, know that tires don’t contain carbon disulfide. Exposure to carbon disulfide comes in other ways, which Blanc has been at the forefront of elucidating. At the University of California San Francisco, he chairs the department of occupational and environmental medicine—a specialty largely concerned with tracing chemical exposures and relating them to human health. He spent the last eight years tracing carbon disulfide, including the stories above, and recently published his findings in an intensive history titled Fake Silk.

Apart from the mysterious effects of the molecule on human nerves and vessels, Blanc said, “the thing that sustained my interest was how everywhere I looked, the trail seemed to go out and intersect and combine in ways that fascinated me.”

The trail began with the explosion of vulcanization in France. Carbon disulfide is a colorless liquid that evaporates rapidly at room temperature. As of 1849, Blanc could only find the compound mentioned in a footnote of the reigning 600-page tome on applied industrial chemistry. By 1851, the updated edition of the book mentioned carbon disulfide on its title page. The author, a chemist of note named Anselme Payen, warned that cold vulcanization can be dangerous to workers on account of the vapors.

Two years later, Payen’s warnings were corroborated by physician Guillaume Duchenne de Boulogne (for whom a major form of muscular dystrophy is named). Duchenne published the first known report of the damage carbon disulfide can do to the nervous system. In a presentation to the Medical-Surgical Society of Paris, Duchenne said that carbon disulfide exposure among vulcanization workers seemed to cause disease “resembling general paresis of the insane,” or syphilis of the brain.