Initial Beliefs and Experiments Explored: What did the scientists initially believe was causing beriberi and how did this guide their experiment?

January 4, 2026 •

4 min read

In the late 19th century, a mysterious and devastating disease called beriberi plagued populations, especially in the Dutch East Indies. At the time, prevailing scientific thought led researchers to hypothesize that beriberi was caused by a bacterial infection, an initial belief that profoundly shaped the direction of their early experiments.

Quick Summary

Early researchers believed beriberi was a bacterial infection and attempted to prove this by injecting blood from sick patients into chickens. A critical flaw in their experimental setup, involving a diet change from whole-grain to polished rice, inadvertently pointed to a nutritional, not bacterial, cause.

Key Points

Initial Hypothesis: Scientists initially believed beriberi was caused by a bacterial infection due to the prevailing germ theory of the era.
Experiment Guided by Belief: This belief led them to design an experiment involving injecting chickens with patient blood, expecting to transmit the disease.
Flawed Design Leads to Insight: The initial experiment was undermined when both injected and non-injected chickens developed the disease, forcing a reevaluation of the hypothesis.
Crucial Observation: The breakthrough came when Christiaan Eijkman observed a correlation between the chickens' diet of polished rice and their illness, which disappeared when they were switched back to whole-grain rice.
New Hypothesis: Eijkman's observation led to a new hypothesis: beriberi was caused by the lack of a vital substance in polished rice, though his initial theory was an 'anti-toxin' rather than a deficiency.
Confirmatory Experiment: Subsequent controlled experiments proved that a diet of polished rice caused beriberi-like symptoms, while a diet of whole-grain rice prevented it.
Shift in Scientific Paradigm: This work led to the concept of vitamins and established that some diseases could be caused by dietary deficiencies, not just infectious agents.

The Dominant Germ Theory Hypothesis

In the 1880s, following the groundbreaking work of pioneers like Louis Pasteur and Robert Koch, the germ theory of disease was ascendant. It provided a powerful new framework for understanding many illnesses, and it was only natural for scientists tackling the beriberi epidemic to look for a microbial culprit. Specifically, researchers in the Dutch East Indies, such as Christiaan Eijkman and his colleagues, hypothesized that a bacterium was responsible for the widespread nerve disease afflicting local populations and military personnel. This was a logical conclusion given the epidemic nature of the illness and the scientific climate of the era.

The Failed Bacterial Experiment

This hypothesis directly guided their initial experiments. The methodology was straightforward: attempt to induce the disease in healthy subjects by exposing them to the supposed pathogen. Eijkman and his team conducted an experiment on chickens, reasoning that the disease might be transmissible.

Initial Step: Injected healthy chickens with blood from beriberi patients, expecting them to contract the disease.
Control Group: A control group of chickens was also established, and was not given the injection.
Unexpected Outcome: Not only did the injected chickens get sick, but so did the control group, undermining the bacterial infection theory.

This confounding result forced a re-evaluation of the initial hypothesis. The bacterial theory was effectively discredited by the results, pushing Eijkman to seek an alternative explanation for the peculiar illness affecting both his test and control subjects.

The Serendipitous Discovery: A New Hypothesis Emerges

Following the failure of the bacterial infection experiment, Eijkman was puzzled. The crucial breakthrough came not from a planned test, but from a mundane observation related to the chickens' diet. He noticed that while all chickens had been eating a nutritious whole-grain rice before the experiment began, the diet was changed to polished (white) rice midway through for cost-saving reasons. After another shift in kitchen staff, the chickens were switched back to unpolished (brown) rice, and their beriberi-like symptoms disappeared.

This casual observation led to a revolutionary new hypothesis: beriberi might not be caused by a germ, but rather by the absence of a vital substance in the diet. Eijkman theorized that polished rice contained a harmful substance that was neutralized by a factor found in the rice's outer husk. While his specific toxin-neutralizing idea was incorrect, it paved the way for the correct nutritional deficiency theory proposed by his successor, Gerrit Grijns.

The Diet Experiment

The dietary hypothesis, although initially based on an incorrect toxin theory, guided the next, more successful experiment.

Experimental Group: Fed chickens exclusively polished white rice, mirroring the diet of many human beriberi patients.
Control Group: Fed chickens nutrient-rich whole-grain brown rice.
Result: The chickens on the white rice diet developed polyneuritis (a condition similar to beriberi), while the brown rice-fed control group remained healthy.

This experiment, replicated and confirmed by other researchers like Grijns and William Fletcher, provided strong evidence that a dietary factor, not bacteria, was the cause of beriberi. The 'factor' was later identified as thiamine, or vitamin B1.

Contrasting Early Beriberi Experiments


Feature	Initial Bacterial Hypothesis Experiment	Subsequent Nutritional Hypothesis Experiment
Central Hypothesis	A bacterial infection causes beriberi.	A dietary deficiency causes beriberi.
Independent Variable	Injection with patient's blood.	Type of rice (polished vs. unpolished).
Dependent Variable	Health status of the chickens (presence of beriberi symptoms).	Health status of the chickens (presence of beriberi symptoms).
Control Group	Chickens injected with saline or nothing.	Chickens fed whole-grain rice.
Experimental Outcome	Injected and control groups both got sick, invalidating the hypothesis.	Polished rice group got sick, whole-grain group stayed healthy, supporting the new hypothesis.
Key Takeaway	Experimental flaw pointed toward an unexpected dietary cause.	Established that beriberi was a deficiency disease, laying the groundwork for vitamin discovery.

Implications for Modern Science

The initial flawed experiment was not a failure but a crucial learning step. It demonstrated the importance of carefully controlling all variables in an experiment, especially when unexpected factors like diet can influence results. The observation-based follow-up experiment is a testament to the power of scientific curiosity and rigorous, controlled testing. It ultimately led to a paradigm shift in medicine, moving beyond the sole focus on germ theory to recognize the critical role of nutrition. The discovery of vitamins began with the focused, iterative process sparked by this early work.

Conclusion

Driven by the dominant germ theory of its time, scientists initially believed that a bacterial infection was the cause of beriberi and designed experiments around this faulty premise. The failure of these early injection experiments, however, inadvertently directed attention to a completely overlooked variable: the diet. A keen observation by Christiaan Eijkman about the chickens' rice supply led to new, diet-based experiments that correctly identified beriberi as a nutritional deficiency, not an infectious disease. This pivotal moment in medical history underscores how a scientific belief, even an incorrect one, can provide the framework for experimentation that, through careful observation, ultimately leads to a revolutionary and accurate discovery.

Visit the Nobel Prize website for more information on the discoveries related to vitamins and beriberi.

Why This Matters Today

The story of beriberi is a classic example of the scientific method in action. It teaches us the importance of questioning assumptions, even widely accepted ones, and the value of meticulous observation. The discovery that a specific dietary component (vitamin B1) was essential for health fundamentally changed our understanding of nutrition and disease. It ushered in the era of vitamin research and has been instrumental in public health initiatives, such as food fortification, to prevent nutritional deficiencies on a global scale. This history highlights how scientific progress often relies on the ability to interpret unexpected results and to revise hypotheses based on new evidence. It is a timeless lesson for all aspiring scientists and for understanding the nature of discovery itself.

Frequently Asked Questions

Initially, scientists believed beriberi was caused by a bacterial infection, influenced by the dominant germ theory of the late 19th century.

Christiaan Eijkman was a Dutch physician and scientist who worked in the Dutch East Indies. His key role involved a series of experiments on chickens that, through a serendipitous observation about their diet, led to the discovery of the nutritional cause of beriberi.

Eijkman's first experiment involved injecting chickens with blood from beriberi patients. When both the injected and control groups of chickens became sick, it disproved the hypothesis that a blood-borne bacterium was responsible.

Eijkman observed that the chickens developed beriberi-like symptoms while being fed a diet of polished white rice, and that these symptoms disappeared when their diet was inadvertently switched back to unpolished whole-grain rice.

The dietary factor was later identified as thiamine, or vitamin B1. Beriberi is caused by a deficiency of this essential nutrient, which is removed when rice is polished.

The discovery was a pivotal moment in medical history, shifting the focus from solely infectious diseases to recognizing that some illnesses are caused by nutritional deficiencies. This led to the discovery of vitamins and the establishment of modern nutritional science.

Eijkman's rigorous experimentation, even when guided by a wrong initial hypothesis, led to a critical observation. The failure of the bacterial experiment paved the way for the dietary hypothesis, demonstrating the power of iterative scientific inquiry.