1. Isometric voluntary contraction in a skeletal muscle is followed by an involuntary post‐contraction of appreciable magnitude and duration in the same muscle. The muscle or rather muscle‐group chosen is the deltoid levator complex, in which the phenomenon has been previously studied. A simple apparatus and means of procedure is described whereby the intensity and duration of the initial stimulus of the voluntary contraction and the magnitude and duration of the post‐contraction can be accurately measured. The simple nature of the experiments renders them suitable for class purposes and, it is hoped, provides a new method of attack upon the problem of muscle contraction. 2. A definite relationship between the intensity and duration of the initial stimulus and the magnitude and duration of the post‐contraction has been established. This relationship can be expressed by the equation A = k log W + c, where A is the angle traversed by the arm in the post‐contraction rise, W is the weight employed for the initial stimulus, and k and c are constants. The normal curve obtained is remarkably uniform for each individual and exhibits four divisions termed α, β, 13, γ, and δ, and three deflexion points termed I., II., and III. 3. If a normal curve be taken, and then after a rest of 20 minutes a similar series of readings be repeated with the same arm, the curve they yield is raised noticeably above the normal throughout, although of the same type. This indicates a direct, ipselateral augmentation of the end‐results. 4. If a normal curve be taken and then immediately a similar set of readings repeated with the same arm, the resultant curve is significantly below the normal throughout, although of the same type. This indicates that the phenomenon described in 3 is preceded by a direct ipselateral inhibition. 5. By plotting the means of from three to six sets of readings, employing the same procedure as for the normal curve, only varying the length of stimulation in each group of sets, it is shown that an initial stimulation of 10 seconds produces the highest and most satisfactory curve in the type of experiment chosen. Shorter or longer stimulation gives a lower curve, and that for 30 seconds is anomalous in certain respects. 6. By stimulating the left arm immediately before taking a reading with the right the resulting curve falls below the normal, showing that the inhibitory effect is also contralateral. This is crossed inhibition. 7. By stimulating the left arm and waiting 17 to 20 minutes before taking each reading with the right, the curve obtained is considerably above the normal, showing that the augmentor effect is also contralateral. This is crossed augmentation. 8. It is shown that if instead of considering the angle traversed by the arm as a measure of the end‐result we take the actual work done against gravity in raising the arm, the work‐curve as produced is of the same type as the, normal curve. 9. A review of the principal investigations into post‐contraction is given. 10. Evidence is adduced to show that volu...

BY FRANK ALLEN. T HE experiments to be described in this paper were suggested by some discussed in a communication 2 to the PHYSICAL REVIEW some years ago. A full description was there given of the method of measuring the persistence of vision which was first used by E. L. Nichols. The essential features of this method are few and simple. In front of the slit of the spectrometer is placed a sectored disk, which, when rotated by an electric motor, interrupts the light causing a flickering of the part of the spectrum under observation. By electrical means the speed of the disk is recorded on paper on a rotating drum, which enables the duration of a single flash of light upon the eye to be determined when the speed of rotation of the disk is such that the flickering just disappears. The duration of these light impulses varies with the luminosity of the spectrum, and, when plotted with the wavelengths of the colors observed as abscissae, gives a persistence of vision curve. I. It was observed 3 that when the eye is protected from light by being blindfolded or by remaining in a dark room, the time of persistence of all color impressions was increased. Experiments were accordingly made to determine how this effect varied with the time of darkness adaptation. Observations of the persistence of vision were made on four colors, red, yellow, green and blue, after intervals of darkness adaptation of one, three, five, ten and fifteen minutes. The wavelengths of the colors observed, and other measurements, are given in Table I. and the results are shown graphically in Fig. I. For convenience in plotting, the ordinates are the differences between the normal readings and those made

HISTORICALIt has long been known that the stimulation of one sense organ influences in some degree the sensitivity of the organs of another sense. But whether the influence is exerted upon the receptors or upon their central areas in the cortex has not been with certainty determined. This behavior of the nervous system may readily be inferred from its synaptical arrangement and intemunciatory constitution whereby all parts are susceptible of communication with each other. These ideas have thus been summsrized by Sherrington (12): "All parts of the nervous system are connected together and n o part of it is probably ever capable of reaction without affecting and being affected by various other parts, and it is a system certainly never absolutely at rest."The two senses which seem to be best adapted for the purpose of measurement are those of hearing and vision. As long ago as 1888, Urbantschitsch (13) observed that sounds of different tones may act differently upon the sensitivity of the visual apparatus for various colors, but no definite quantitative relation between sound and color was detected by him. In later investigations Lazarev (11) concluded that the visual sensibility of the retinal periphery, that is of rod vision, increased under the influence of acoustical stimulation of the ear. Yakovlev (15) found that stimulation of the ear by sound conspicuously enlarged the area of the field of cone vision especially for green light. Kravkov (8) observed that under the influence of sound the critical frequency of flicker of white light increases for central or cone vision, and diminishes for peripheral or rod vision.In a recent investigation Yakovlev (16) has studied in much detail the influence of acoustic stimulation, both by musical tones of frequency 780 cycles per second and noises of 75 decibels in loudness, upon the limits of the areas of the retinal fields for extreme red, orange-red, green, and blue colors. The colors were not spectral but were obtained from Wratten color filters. The maximum transmissions of the filters were at 700 m/~, 680 m#, 540 m~, and 440 m~ respectively. Two observers were employed and from their measurements the following results were obtained. Under the influence of both tones and noises the color field for extreme red was unaltered, that for orange-red was dlmluished, and those for green and blue enlarged in area. Noise was more effective as a stimulus than musical tones, possibly because of its greater intensity, and under its influence the color fields were diminished and enlarged to the greatest extent.In a more detailed research Kravkov (9) has investigated the influence of acoustic stimulation of the ear upon the light, or rod, and the color, or cone, sensibility of the 105

No abstract

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.