Some Constituents of the Poison Ivy Plant (Rhus Toxicodendron)

In Short

This 1906 doctoral dissertation details the chemical breakdown of the poison ivy plant (Rhus toxicodendron). Submitted to Johns Hopkins University by William Anderson Syme, the work isolates and identifies key plant constituents while investigating the true chemical nature of its elusive toxin. By systematically fractionating crude ether extracts, running elemental analyses, and performing controlled self-experimentation, Syme dispels prevailing myths regarding volatile plant poisons. His work established that the toxic principle is a non-volatile, resinous glucoside compound, while simultaneously demonstrating the therapeutic efficacy of potassium permanganate as an immediate topical antidote.

The Story

The investigation begins with an examination of existing botanical and pharmacological literature concerning the genus Rhus. Early historical accounts had proposed conflicting theories regarding the plant’s toxic properties: nineteenth-century researchers such as Khittel claimed to find a volatile alkaloid, while Maisch attributed the irritation to a volatile "toxicodendric acid." However, clinical observations by Dr. Franz Pfaff later proved that the true skin irritant is non-volatile, identifying Maisch’s alleged poison as ordinary acetic acid. Building upon Pfaff’s findings, Syme seeks to systematically isolate, purify, and characterize the non-volatile poisonous principle, alongside the plant’s secondary chemical compounds.

To begin the experimental process, Syme receives a large shipment of crude ether extract processed from poison ivy leaves and flowers. The dense, dark tar releases an intense, nauseating odor of crushed green leaves upon opening. Despite wearing a protective cotton mask and heavy rubber gloves, Syme contracts severe facial rashes during the initial handling. Undeterred, he subjects the raw material to vacuum distillation, esterification, solvent extractions, and lead-acetate precipitations.

As he divides the complex mixture into distinct fractions, Syme isolates several major non-toxic chemical constituents. He successfully identifies gallic acid through its reaction with potassium cyanide and ferric chloride, and confirms its identity by synthesizing its anhydrous ester. Next, he extracts a deep yellow dye, identifying it as the plant pigment fisetin. Further chemical tests demonstrate the presence of the rare methyl pentose sugar rhamnose, an unexpected discovery as free pentose sugars were thought not to exist naturally in such plant structures.

Syme then turns his attention to the core question of the research: the physical structure of the poisonous principle itself. He discovers that the toxic compound forms an ether-soluble lead salt, allowing him to separate the active poison from non-poisonous material via Soxhlet extraction. Distillation of the purified tar with acetic acid confirms that the poison does not volatilize. When he subjects the purified poisonous gum to acid hydrolysis, it breaks down into gallic acid, fisetin, and rhamnose, proving that the toxin is a complex glucoside—termed toxicodendrin—which loses its irritant properties upon chemical breakdown.

Throughout his investigations, Syme tests the various isolated fractions directly upon his own skin to monitor toxicity, using a finely drawn glass rod to apply microscopic drops. To treat the resulting eruptions, he evaluates common remedies, criticizing traditional lead acetate washes for simply redepositing the unstable toxic salt back into the skin. Instead, Syme demonstrates that an oxidizing agent—specifically potassium permanganate—completely destroys the poison on contact. He concludes his treatise with a clear, standardized protocol for isolating pure toxicodendrin and a brief autobiographical sketch.

How It Unfolds

Surveying the literature Syme reviews past efforts to identify the active principle in Rhus toxicodendron, contrasting early claims of volatile alkaloids and toxic acids with Pfaff’s evidence of a non-volatile skin irritant. He establishes that previous researchers often mistook acetic acid impurities for the active poison.

Fractionating the crude extract Working with a massive ether extract of poison ivy leaves, Syme separates the raw tar into water-soluble and solvent-soluble fractions. Despite using rubber gloves and cotton face masks, he develops painful facial eruptions from the pervasive vapors and dense resins.

Identifying gallic acid and fisetin Through fractional precipitation with lead acetate, Syme separates non-poisonous compounds from the crude material. He isolates pure gallic acid by preparing its crystalline barium and sodium salts, and isolates the vibrant yellow plant pigment fisetin.

Confirming the presence of rhamnose Syme isolates the methyl pentose sugar rhamnose from the plant extracts through color reactions and dehydration tests yielding methyl furfurol. This proves that the sugar exists in a free state or within a plant glucoside, challenging prevailing botanical assumptions.

Isolating the toxic glucoside By extracting the lead precipitate with ether in Soxhlet apparatuses, Syme isolates the refined poisonous resin, naming it toxicodendrin. Subsequent acid hydrolysis yields gallic acid, fisetin, and rhamnose, demonstrating that the toxin is a complex glucoside that loses its toxicity when broken down.

Demonstrating a permanganate cure Syme tests the potency of the isolated fractions by applying small drops directly to his own skin with a glass rod. When severe rashes develop, he successfully neutralizes the irritation by thoroughly rubbing a potassium permanganate solution into the affected areas.

The People

• William Anderson Syme

A doctoral candidate in chemistry at Johns Hopkins University who serves as both investigator and experimental subject. He seeks to isolate the active chemical constituents of poison ivy, enduring repeated, painful skin eruptions to verify the toxicity of his fractions and prove the efficacy of his proposed antidote.

• Dr. S. F. Acree

A professor of chemistry at Johns Hopkins University who suggested the research project to Syme. He guides the experimental design, advising Syme on the complex fractionation steps required to isolate organic plant compounds.

• Dr. Franz Pfaff

A predecessor scientist whose foundational clinical research disproved the long-held "volatile acid" theory of poison ivy toxicity. His work provides the baseline assumption for Syme’s experiment: that the irritant is a non-volatile compound capable of causing severe skin and renal complications.

• Professor J. M. Maisch

A nineteenth-century pharmaceutical chemist who famously claimed that "toxicodendric acid" was the poisonous agent in poison ivy. His historical findings serve as a primary theoretical counterpoint that Syme and Pfaff systematically disprove.

In Its Own Voice

"When the bottle was opened, there seemed to be an escape of a vapor, and a nauseating odor suggesting crushed green leaves pervaded the atmosphere."

Syme notes the intense physical presence of the crude plant extract upon starting his laboratory experiments.

"A very small drop of this solution applied to the skin on the end of a glass rod which had been drawn out to a point caused an eruption in about thirty-six hours."

The author describes the rigorous, self-sacrificing method used to determine which isolated fractions contained the active toxin.

"All cases of poisoning developed on the writer were easily cured with potassium permanganate."

Syme confirms the practical success of his chemical antidote after repeatedly testing isolated poisonous resins on his own arms and face.

What It's Really About

At its core, this dissertation demonstrates the rigorous application of modern organic chemistry to dismantle long-standing medical folklore. For decades, botanical and medical authorities believed that poison ivy emitted an invisible, volatile gas or a light, drifting acid that carried through the air to affect passersby. Syme’s research dismantles these misconceptions by applying structured isolation methods, proving that the plant's danger lies in a sticky, non-volatile resinous glucoside.

Beyond its specific chemical conclusions, the text highlights the necessity of self-experimentation in early twentieth-century pharmacology. Syme serves as his own test subject, bridging the gap between benchtop organic synthesis and clinical application. The research transforms a dreaded natural hazard into a series of identifiable, predictable organic molecules.

Why Read It Today

This work offers readers a clear window into early twentieth-century American chemical research. Unlike modern academic papers, which are often obscured by dense jargon, Syme’s prose is direct, transparent, and narrative-driven. It reads as a concise detective story, where the scientist systematically eliminates chemical suspects until the true agent is exposed.

Readers interested in the history of science, botany, or medical research will appreciate the author's meticulous attention to detail and unpretentious delivery. The text candidly illustrates the physical hazards of historical laboratory work—from handling toxic lead precipitates and toxic gases to enduring intentional, self-inflicted poison ivy rashes. While the narrative consists entirely of laboratory procedures and chemical equations, Syme’s personal involvement gives the technical work a distinct human dimension. His practical discovery—that potassium permanganate oxidizes and neutralizes the toxic resin—remains an intriguing historical footnote in the study of contact dermatitis remedies.

<ElicitationsGroup message="To explore the historical background or scientific methods in this work:">

<Elicitation label="Examine the early chemical methods used to isolate plant glucosides" query="Explain the 20th-century chemical methods used by William Syme to isolate plant glucosides, including lead acetate precipitation and Soxhlet extraction."/>

<Elicitation label="Compare historical and modern remedies for poison ivy exposure" query="Compare the historical use of potassium permanganate and lead acetate for poison ivy dermatitis with modern medical treatments."/>

</ElicitationsGroup>