In anatomy and neurophysiology, this is the finding that the anterior spinal nerve roots contain only motor fibers and posterior roots only sensory fibers and that nerve impulses are conducted in only one direction in each case. The nature and the physiology of the phenomena were described independently by the British anatomical scientist Sir Charles Bell and the French physiologist François Magendie, later confirmed by the German physiologist Johannes Peter Müller. History The findings were described independently by two professors working in different medical paradigms: by Sir Charles Bell an anatomist and Francois Magendie – a pathophysiology and physiology professor . Their independent observations were 11 years apart. Another definitive experimental proof was given nine years after Magendie's experiments by Johannes Peter Müller during a vivisection of a frog in 1831. Bell's discovery In 1811 in a self-sponsored and published pamphlet Charles Bell referred to the motor functions of nerve fibers exiting the ventral roots of the spinal cord but did not mention the sensory functions of the dorsal roots. That was in part because his studies were dissectionist and not vivisectionist; pain is elicited and detected best in a conscious animal. A dead, or rendered unconscious, animal would not produce the desired effect when posterior horn fibers, responsible for sensation and transfer of noxious signals, are stimulated. Bell's nephew, John Shaw travelled in 1812 to Paris where he presented Bell's system to the French anatomists. Reportedly Shaw staged a demonstration on the facial nerves of a donkey without the intended effect. Magendie's puppies experiment Eleven years later, Magendie announced in the magazine Journal de physiologie expérimentale et de pathologie his discovery that the motor neuron fibers exit from the anterior root and the sensory neuron fibers from the dorsal root: "(trans)section of the dorsal root abolishes sensation, (trans)section of ventral roots abolishes motor activity, and (trans)section of both roots abolishes both sensation and motor activity." Magendie gave the first complete description of the experimental proof of the Bell–Magendie law. His experiments were public, often conducted in the presence of medical students and curious citizens. That particular experiment was conducted by severing the anterior and posterior roots of spinal nerves in different combinations of several dogs in a litter of puppies. Stimulation of the posterior roots caused pain, and stimulation of the anterior – movement. The experiment was criticized for its cruelty by the Paris and London Humane societies. Detailed