Some date back to the 15th century. Most are speci c to the 19th century - time when the germ theory" won the battle. The quests in searching for the causes of nutrition-de cient diseases was masked by the overwhelming con dence in one germ, one disease" theory. Pelle" agra" italian for skin" rough". Appears rst as a skin rash; skin then crusts and peels away. Clinical symptoms 4d"s: dermatitis, diarrhea, dementia, and death. 1909 epidemic in us: reported in 26 states. 1912 high fatality rates; e. g. 40% in s america. 20th century 3m cases in the us and 100,000 deaths. Belief that pellagra was an infectious disease speci c to the poor. By 1939 evidence established that disease was due to niacin-de ciency (a water-soluble b vitamin vitamin b3) Niacin needed for normal oxidative metabolism of sugars. Lack of niacin implies sugars are not able to be metabolized - illness.