We continued and expanded our investigation of non-electrical signs of excitation processes in the nervous system. Using isolated spinal cord preparations of the bullfrog and newborn rat, we found that afferent nerve impulses arriving at the spinal cord evoke a rapid rise in the temperature of the cord. A thorough examination of the observed temperature rise has indicated that transmission of nerve impulses across the synapses at the terminals of the sensory fibers is accompanied by generation of a considerable amount of heat in the substantia gelatinosa. This discovery of the """"""""thermal response"""""""" of the spinal cord has given us a new, useful tool for studying the effects of various chemicals on synaptic transmission. We also examined excitation processes in the bullfrog retina by using our thermal detectors and piezoelectric sensors. We found that the photoreceptors in the dark-adapted retina are capable of releasing thermal energy which is more than one million times as large as the energy of the light pulse used for stimulation. Furthermore, we found it possible to analyze the processes of synaptic transmission in the retina by taking its mechanical responses as an index.
