a physiological experiment that led to the discovery of central inhibition, that is, the inhibitive processes in the central nervous system. During experiments conducted on a frog in 1862,1. M. Sechenov observed that the reflex of the spinal cord (bending of the legs when a frog is immersed in a weak acid solution) is depressed upon the chemical or electrical stimulation of the thalamic region. This experiment disproved the concept that the regulatory functions of the brain and spinal cord are ensured only by certain excitory processes. It was proved that in addition to excitory interactions there exist qualitatively specific inhibitive interactions between nerve elements. Sechenov’s inhibition, like other phenomena of centra! inhibition, is effected by specific inhibitive neurons and synapses present in the brain and spinal cord.