In the early 1880s, Kanehiro Takaki observed that Japanese sailors (whose diets consisted almost entirely of white rice) developed beriberi (or endemic neuritis, a disease causing heart problems and paralysis), but British sailors and Japanese naval officers did not. Adding various types of vegetables and meats to the diets of Japanese sailors prevented the disease, (not because of the increased protein as Takaki supposed but because it introduced a few parts per million of thiamine to the diet, later understood as a cure).
Is there an answer to this question (If it cannot be answered, say "unanswerable"): Who made the observation that the Japanese sailor's diet was the cause for them developing beriberi?
Kanehiro Takaki