The isolation and identification of the anti-black tongue factor

A study from 1937 showing supplementing niacin cures black tongue in dogs just as well as feeding them liver. Other studies from the time are also mentioned such as one that shows rats supplementing nicotinic acid (niacin) lived longer.

Overview

This landmark 1937 paper by Elvehjem, Madden, Strong, and Woolley (Journal of Biological Chemistry) established that nicotinic acid — niacin / vitamin B3 — is the “anti-black tongue factor” that cures black tongue disease in dogs. The paper confirmed that synthesized nicotinic acid, not liver extract, was the active compound responsible for the curative effects long associated with liver supplementation.

What Is Black Tongue Disease?

Black tongue in dogs was a well-characterized nutritional deficiency disease in the 1930s, analogous to pellagra in humans. Affected dogs developed inflamed, dark lesions on the tongue and oral mucosa (hence “black tongue”), along with salivation, gastrointestinal inflammation, and eventual death if untreated. For years it was known that feeding dogs raw liver cured the condition, but the active component was unknown.

The Isolation

The 1937 paper describes systematic fractionation of liver and yeast to isolate the active compound. The researchers identified it as nicotinic acid — a molecule already known to chemists as a derivative of pyridine, but not previously recognized as a vitamin. They demonstrated that pure synthetic nicotinic acid at small doses cured black tongue as effectively as liver.

This was a pivotal moment: nicotinic acid was established as the vitamin responsible for preventing pellagra in humans and black tongue in dogs, and could now be synthesized and given in pure form.

The Rat Longevity Note

The paper also references a separate study showing that rats supplemented with nicotinic acid lived significantly longer than unsupplemented controls — an early data point suggesting niacin’s effects extend beyond simple deficiency correction.

Historical Significance

The isolation of the anti-black tongue factor as nicotinic acid is one of the foundational discoveries in vitamin history. It opened the research path to understanding niacin’s pharmacology at therapeutic doses — doses far above the nutritional requirement — including its effects on lipid metabolism, GPR109A activation, and inflammatory modulation.

Note on naming: The term “niacin” is used loosely for both nicotinic acid (the compound isolated in this paper) and niacinamide (nicotinamide). The anti-black tongue factor was specifically nicotinic acid. The two forms have distinct pharmacological profiles and are not interchangeable for all purposes.