Beri-Beri

Eijkman noticed that some of the chickens living at the research station contracted beriberi-like symptoms. 

Eijkman tried to correlate the onset of the sickness with environmental variables and noticed that the chicken’s got sick only after a shipment of their red rice failed to arrive, and they were fed higher grade polished white rice instead.  (In nature, rice is covered by a red or brown husk. )

Polishing removes the husk and allows rice to be stored much longer with a lesser risk of spoilage.)  When the superintendent of the research station noticed that they were being fed polished white rice he reordered a shipment of unhusked red rice to reduce his costs. 

Eijkman noticed that the health of the chickens recovered after they were fed the unhusked rice. Most people would have shrugged off this observation, but Eijkman recognized its significance.