Abstract
1. The action of ultrasound was studied on the sciatic nerve of a frog, the spinal cord of a toad, and the brain of a bullfrog tadpole and a frog. The results were compared with the effect of temperature.
2. The action potential of a myelinated nerve was enlarged by irradiation with ultrasound of about 16 W/cm.2, but it was inhibited by irradiation with that of higher intensity.
3. The reflex discharges of the spinal cord were increased by irradiation with ultrasound of about 3 W/cm.2. But they were inhibited at higher intensity (beyond 6.83 W/cm.2).
4. The brain wave was augmented by irradiation with weak ultrasound, but they were decreased by repeated irradiation.
5. It was concluded that ultrasound has a stimulative action at low intensity, but has an inhibitory action at high intensity on the nerve tissues and the muscle. However, when ultrasound with a stimulative action was repetitively applied, it eventually produced an inhibitory action.
6. Spontaneous discharges appeared on the spinal ventral root by ultrasonic irradiation. Up to a certain ultrasonic intensity, an inverse linear relation was found between the intensity and the latent period of the discharge.
7. The rise of temperature was measured in a frog muscle during and after ultrasonic irradiation. It was found to be less than 10°C. at the ultrasonic intensities which produced a stimulative action.
8. By raising the temperature of Ringer's solution, the effect of temperature was studied on the spinal reflex activity. The results were entirely different from the ultrasonic actions on the spinal cord. It was therefore presumed that the main role of the actions of ultrasound is not played by a rise of temperature, but by the other actions of ultrasound.
