The Bell Megendie Law 1811 – Two Scientists, One Law

Describing the brain, neuroanatomist Marian Diamond writes: "The brain is a three-pound (1.36-kilogram) mass capable of comprehending a universe a hundred billion light-years wide.”

In humans, the brain, spinal cord and nerves together form the nervous system. Sensory neurons (nerve cells) are activated by various stimuli, such as touching the skin. Motor neurons connect the nervous system to muscles and are used to trigger muscle movements.

A Historical Scientific and Ethical Dispute

One of the important laws in medical history, the Bell-Magendie law, states that sensory nerves enter the spinal cord dorsally (from the back of the spinal cord). Motor neurons, on the other hand, leave the spinal cord ventrally (from the front). Scottish anatomist Charles Bell's privately circulated book Idea of a New Anatomy of the Brain (1811) contains references to experimental work on the motor functions of ventral spinal nerves. Although considered a foundation of clinical neurology, it did not conclusively establish the sensory functions of dorsal nerves. 

In 1822, working independently of Bell, French physiologist François Magendie discovered that the ventral root was associated with motor functions and the dorsal root with sensory functions. Through experiments and anatomical examinations in mammals, he showed that systematically destroying particular nerves could produce paralysis or loss of sensation. Although Bell and Magendie argued fiercely about who had actually discovered the law, it is now named after both scientists.

Regulating Animal Experiments

Magendie's public animal experiments led to the introduction of a bill in England banning animal abuse. In one incident, Magendie dissected a living greyhound nailed down by its ears and feet, cutting away half its face. The dog was kept alive for further dissection the following day. Even doctors who supported using animals in medical research thought Magendie's attitude towards animals was extremely careless and unscrupulous.

The dispute between Bell and Magendie also had an ethical dimension. Magendie was frequently criticised for his animal experiments, and in some cases was accused of inflicting unnecessary pain and torture. Bell criticised his attitude. This represents an important turning point in medical history, because these debates brought greater attention to animal experimentation and the importance of ethical issues.

Description of the article image: A rear view of the spine with nerves shown in green. Sensory nerves enter the spinal cord (shown in orange) from behind, near the person's back. Motor neurons emerge from the front of the spinal cord, towards the person's abdomen.

Historical figures mentioned in the article: Sir Charles Bell (1774–1842), François Magendie (1783–1855)

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