In cats the spinal cord was semisected above the sacral enlargement and time allowed for degeneration of descending fibers. In the acute expt. the brain was pithed, the quadriceps muscles were arranged for recording, and the thoracic aorta was prepared for injs. Tests of relative sensitiveness of the neurones on the 2 sides of the cord, made by injecting strychnine, acetylcholine and strong sodium carbonate soln., and by inducing asphyxia, revealed greater effects on the semisected than on the intact side of the cord. The inference is drawn that, as neurones of the superior cervical ganglion are sensitized by severance and degeneration of nerve fibers which routinely deliver impulses to them, neurones of the spinal cord are analogously sensitized by partial exclusion of their normal nerve connections. Skeletal muscle is sensitized by section of penultimate motor neurones, thus resembling sensitization of smooth muscle sensitized by section of preganglionic sympathetic fibers.