SYNOPSIS.IN this communication a description is given of the method of studying the tactile sensation by measuring the critical frequency of percussion of air pulses when they become fused into a continuous sensation. By applying the method to the index finger of the right hand, a normal curve is obtained for a range of air pressures from 1P0 cm. to 5 0 cm. of mercury. The measurements show that there are two fusion points vof intermittent stimuli, which are designated superficial and deep touch. By plotting the time values of the critical frequency of percussion against the logarithms of the air pressure, the curves become straight lines conforming to the equation D=--K log P+C. Each curve consists of two straight lines of different slope, which are analogous to similar effects in light and sound perception. In light the effect has been attributed to rod and cone vision. It is shown that it must be referred rather to some property that all sensory nerves possess in common.The effect of fatigue upon the critical frequency of percussion was measured, and its curve was found to lie above the normal but exactly similar to it. This is also the same as in light and sound.Reflex enhancement of the tactile sensation was produced by tightly bandaging the third digit while the critical frequency of percussion was measured for the index finger. The measurements showed that the enhancement curve lies below the normal, similar to the effect produced in one eye by fatiguing the other. Reflex enhancement from the other fingers was also obtained with like results. Similar effects were obtained for both first and second fusion points.The curves for each fusion point converge and intersect at what is termed an " equilibrium pressure," where reflex and fatigue effects appear to vanish.The presence of direct fatiguing (afferent) and reflex enhancing (efferent) effects in the tactile sensation is applied to tactile contrast and after images; WEBER'S law is discussed and shown to be the difference between two opposing physiological processes whose laws are unknown.

The construction and performance of an amplifier employing the interaction between two streams of electrons having different average velocities are described. Gain of 33 db at a center frequency of 255 Mc has been observed with bandwidth of 110 Mc between 3 db points.

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