What evidence shows that pellagra was not a germ?

The evidence that pellagra was not caused by a germ primarily comes from the observation that the disease's prevalence was closely linked to diet rather than infectious transmission. Researchers, notably Dr. Joseph Goldberger, demonstrated that pellagra could be prevented and treated with a diet rich in niacin (vitamin B3) and proteins, which was lacking in the diets of those affected. Additionally, the disease did not spread in a typical infectious manner, as outbreaks were associated with specific socioeconomic conditions rather than person-to-person contact. This led to the conclusion that pellagra resulted from nutritional deficiency rather than a germ.