have to inquire, for instance, what effects sounds which stimulate the auditory organs and cause the animal to become alert, watchful, yet make it remain rigidly motionless, have on the primary organic rhythms of the organism, such as the heart-beat, respiration, and peristalsis. It is also directly in the line of our investigation to inquire how they affect reflex movements, or the reaction time for any other stimulus-what happens to the reaction time for an electrical stimulus, for example, if a loud noise precede or accompany the electrical stimulus. III. THE INFLUENCE OF SOUNDS ON REACTIONS TO OTHER I. Influence of sound on respiration and visual reactions.— Observations described in my earlier paper prove that respiration is modified by sounds, and it was also noted that the attempts of a frog to seize a moving object are reinforced by the sound of a tuning fork.1 2. Influence of sounds on tactual reactions.-A more detailed study has been made of the influence of sounds on tactual reactions and of the significance of the temporal relations of the stimuli. A reflex movement of the leg was chosen as an indication of the action of the stimuli and the influence of sounds was observed under the following conditions. A frog was placed on a saddle-like holder and kept in position by linen bands over the back and a wire screen cap over the head, as shown in Fig. 4. Under these conditions the hind legs usually hang free and limp and any movement which may be made by them in response to a stimulus can be read in millimeters from a scale, attached to the holder. This method of measuring the value of stimuli in terms of leg reflex has been used by several other investigators, most recently by MERZBACHER. In this connection it is of interest to note that neither MERZBACHER nor EWALD were able to detect movements of the leg of the frog in response to sounds. Even the croaking of another frog near by had no apparent effect. 2 11. c. p. 634. "MERZBACHER, L. Ueber die Beziehungen der Sinnesorgane zur den Reflex. bewegungen des Frosches. Pflüger's Arch., 81, 254, 1900. I found it desirable, as did MERZBACHER, to observe the movements of a shadow of the leg on the scale and thus read the amount of movement, rather than to watch the leg itself and attempt to project it upon the scale. As is indicated in the figure the auditory and tactual stimuli were given automatically by means of a swinging pendulum (P) which was held in position by the magnet a until released by the experimenter. Early in its swing the pendulum turned the key m thus completing a circuit which caused the auditory stimulus to be given; later in the swing the key n was turned, and the tactual stimulus thus given through the magnetic release of the lever l. The interval between the auditory and the tactual stimuli could be varied from .1" to .9" by change in the position of the key n. For giving the two stimuli simultaneously a double hand key was employed.1 The auditory stimulus was either the sound of a quick hammer blow or the ringing of an electric bell for a certain interval. Figure 4 shows the bell. It was placed 80 cm. from the frog, and in order that the influence of vibrations might be avoided was suspended from the pendulum frame. When the hammer was used it was placed 60 cm. from the frog, on the pendulum table. The frog and the apparatus for tactual stimulation occupied a separate table which was not disturbed by the jars of the pendulum table. The tactual stimulus was given by a rubber cone, T, Fig. 4, 2 mm. in diameter at its apex. This rubber point, after the electric release of the lever to which it was attached, struck the frog at the middle point of a line drawn between the posterior margins of the tympana. The intensity of the stimulus could be varied by weighting the lever (see w in the figure). Under the conditions of experimentation described above, a tactual stimulus regularly causes a reflex movement of the 1A full account of this method and the results of a study of the phenomena of auditory-tactual reinforcement and inhibition may be found in Pflüger's Archiv, Bd. 107, S. 207, 1905, under the title "Bahnung und Hemmung der Reactionen auf tactile Reize durch akustiche Reize beim Frosche." In this connection I mention only such aspects of the investigation as bear on the subject of audition. suspended leg, which varies in amount with the state of the animal and the strength of the stimulus. A sound, on the contrary, never causes the slightest movement, and that no matter how loud or high it be. This makes it possible to study the influence of sounds on tactual reactions, under different temporal relations of the stimuli, for even when the sound precedes the touch there is no reaction until after tactual stimulation. The results now to be presented were given by the green frog, but test experiments indicate that both the leopard and the bull frog are influenced in similar manner by sounds. The experimental procedure was as follows. After an animal had been placed in the proper position and had ceased to struggle to escape, reactions to stimuli were taken in pairs regularly at half minute intervals, first a reaction to the tactual stimulus alone, then a reaction to the same intensity of touch when accompanied or preceded by an auditory stimulus. pause. The series consisted of 50 pairs of reactions taken without So far as the frog is concerned there seems to be nothing undesirable in long series, for there is no indication of fatigue, and so long as the animal is kept moist and in a comfortable position it does not often struggle to escape. The advantage, for the purposes of this investigation, of taking the reactions in pairs is obvious. It permits us to compare directly the reactions of each pair, and to note at once whether the auditory stimulus has reinforced or inhibited the tactual reaction. During a series the intensity of the tactual stimulus was changed as conditions demanded, but for any one pair of reactions it was always the same. It not unfrequently happened that an intensity which at first caused only slight movement of the leg, later in the series uniformly brought about a maximum contraction, or the reverse might be true, and since the maxi Fig. 4. Auditory-tactual apparatus. (Drawn by Dr. Wм. E. HOCKING.) P, pendulum; p, contact point of P; b, attachment for electro-magnet, a; m, key for electric bell circuit; B, electric bell; n, key for magnet circuit of touch apparatus; K, hand-key for release of pendulum and temporary closing of electric bell circuit; k1, k2, 3, keys in circuits; e, f, g, magnetic release for touch apparatus; /, pivoted lever bearing rubber cone, T, and weights, w. mum amount of movement left no opportunity for judging of the influence of the auditory stimulus it was always necessary in such cases so to alter the intensity of the tactual stimulus that a medium reaction would result. The animals seldom struggled during experiments, but if too firmly bound they became irresponsive to the stimuli.1 It was therefore necessary to place them carefully in position, and then, after they had ceased to struggle, to draw the linen bands over them just tightly enough to prevent change in position. For the purpose of excluding the influence of visual stimuli a wire screen cap covered with black cloth was put over the head. This served to help keep the frog in the proper position as well as to exclude visual stimulation. TABLE I. THE INFLUENCE OF SOUND ON THE TACTUAL REACTIONS OF THE GREEN FROG. Auditory and Tactual Stimuli Green frog A. Tactual Stimulus Alone |