The discovery of vitamin B1 began with a search for microbes. In the late 1800s, microbes were the hot new idea in medical science: Louis Pasteur had recently linked disease to germs, and doctors were looking for microscopic explanations for all kinds of ailments. Even when those ailments had nothing to do with germs at all.
Take beriberi for example—a common disease that could cause nerve damage or heart failure. Beriberi had already been linked with diet, but when Dutch scientists started looking for its cause, they thought they might be looking for a microbe. To find that microbe, they tried infecting small animals (rabbits, monkeys, chickens) with the disease by exposing them to blood and urine from animals with beriberi.
When they did that, something strange happened. The rabbits and the monkeys never got sick. But the chickens, kept in coops at a research institute in Indonesia, did get sick. The problem was, they all got sick—not just the chickens that had been exposed to blood and urine, but the control groups, too. Christiaan Eijkman, who was running the experiment, bought more chickens and tried to infect some; he separated them from one another; they all got sick. Then, somehow, they got better.