I. Studies on Vibration Sensation. II. Heat Production of Slow and Fast Contractions of a Crustacean Muscle with Double Motor Innervation

Apparatus and a method are described for testing the responses in men to mechanical vibrations of different frequencies. This method has been applied to over 600 men. In the whole group the thresholds at all frequencies increase with the age of the subjects. Similarly the upper frequency limit to which there is a response falls off with age. Half of the men received vitamins for a period of approximately one year, half did not. In the older age group, those receiving the vitamins were found to have lower thresholds than those who did not, but the difference is below the level of statistical significance. A method has been developed for measuring the heat produced during sustained contractions, of both the slow and fast types, of the closer of the cheliped of the crayfish Cambarus clarkii. The contractions occur in the same muscle fibers. Any heat produced by, or accompanying, the muscle action current alone is less than can be measured by the method used. On repetition, both types of contraction become more efficient. The slow contractions are more efficient than the fast, both when the mechanical effects of the contraction are dissimilar and when they are made as alike as possible.