. Physical researches on sensation [by] Frank Allen [and others]. s is permissible,it appears that normal tactile sensations differ with indi^^duals insensitiveness. No doubt the customary manual occupations have theirinfluence. The disparity in age, one being double the other, betweenthe authors may likewise account for the difference. It also suggeststhat study of many individuals may bring to light phenomena of touchanalogous to anomalous vision and colour blindness in sight. It isespecially to be noted, that though only one curve obtained by Allenis given here, yet sufficient measurements
. Physical researches on sensation [by] Frank Allen [and others]. s is permissible,it appears that normal tactile sensations differ with indi^^duals insensitiveness. No doubt the customary manual occupations have theirinfluence. The disparity in age, one being double the other, betweenthe authors may likewise account for the difference. It also suggeststhat study of many individuals may bring to light phenomena of touchanalogous to anomalous vision and colour blindness in sight. It isespecially to be noted, that though only one curve obtained by Allenis given here, yet sufficient measurements under fatigued and variousenhanced conditions of the tactile sensation were obtained by him toverify and confirm the more extended measurements of Hollenberg. The normal curves all conform to the equation D=-KIogP+C, Oil the Tactile Sensorv Reflex where D is the time interval at the critical frequency of percu(>8ion, Pthe pressure of the air. and K and (_ are constants tlepending upon thenature of the physiolo<:i(al processes involved and the experimental. 0002 •30 -40 Log P. Fio. 2.—Normal tactile |>orsist^ncy curves reduced to linetu- fonn. method of investigation. It is the constants that vary from curve tocurve, and in the two parts of tiie indivi^luai curves. The negativesign indicates tiiat the duration of impressions at the critical fre(iuencyof percussion decreases in direct proportion to the increase of thelogarithm of the air pressure. 360 Allen and Hollenberg For the normal (vaseline) curve of Hollenberg, fig. 2, curve C, theequations with numerical values of the constants, K and C, for the upperand lower branches of the curve respectively, are : D= —00833 log P + -0089D=--0158 logP + -0135. In vision, when the logarithms of the intensity of illumination, I,are plotted against the reciprocals of the duration of the sensation atthe critical frequency of flicker, D, we obtain a similar equation : ^=KlogI+C, which is known as the Ferry-Porter law. This la
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