. Physical researches on sensation [by] Frank Allen [and others]. -0 0-099 I I (i-0( 0-00240 000243 1 the other, it was now ((Mite appannt tiiat there wi-re two j)oints offusion of interrupted stimuli. This was verified hy starting the rotationof the disk very slowly at some pressure of the air until one fusion {)ointwas reached. The speed was then increased and the sen.*yition againbecame interrupted. On further increasing the speed a second pointwas reached where there was apparent fusion of the stimuli. Tiiis secondfusion point is not of the sjime nature as the first ; it was less sjiti
. Physical researches on sensation [by] Frank Allen [and others]. -0 0-099 I I (i-0( 0-00240 000243 1 the other, it was now ((Mite appannt tiiat there wi-re two j)oints offusion of interrupted stimuli. This was verified hy starting the rotationof the disk very slowly at some pressure of the air until one fusion {)ointwas reached. The speed was then increased and the sen.*yition againbecame interrupted. On further increasing the speed a second pointwas reached where there was apparent fusion of the stimuli. Tiiis secondfusion point is not of the sjime nature as the first ; it was less to speak, hut still it was a definitely measurable point of making reaciings. then-fore, care was taken to observe and recordwhich fusion point was under observation. Consequently the problemresolved itself into the investigation of the relation between the critical 356 Allen and Hollenberg frequency of percussion and the air pressure at the first fusion pointand at the second. The significance of these two fusion points we do not at present. 0002 lOcm 1-4 ■8 22 26 30 3-4 3-8 42 Pressure. Fig. 1.—Normal tactile persistency curves. understand. The first quite probably represents a superficial, and thesecond a deep tactile, sensation. The normal curves were obtained in the manner already described,and the measurements are given in Table I. The corresponding curvesare plotted in fig. 1. In the first investigation of the first fusion pointthe ordinary dry finger was used. Readings were obtained mth diffi- Oil the Tactile Seniiorv Reflex 357 c ulty, especially at tlit- lii^lur pn^ures, beeauHf of the tlryiug effect ofthe air pulses upon the skin, \shieh quickly hccaiiic dry and hard, andtherefore less sensitive. This is shown in the rt]t£ure by its positionrelative to the other normal curves, .Since the tlrying effect was dis-concerting, it was decided to use water with which to moisten the fingerbefore each reading. \cry consistent results were easily obtai
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