INERTIA AS RELATED TO CONSCIOUSNESS 91 



Speaking of pressures applied to the skin Pro- 

 fessor Sherrington says,* " Pressure applied to the 

 skin evokes a sensation which does not subside 

 the sensation continues." 



The positive after-sensation of pain persists for 

 a much longer time than does that for touch ; that 

 is, in my terminology, the katabolic inertia of the 

 algesic sensory apparatus is greater than that of 

 the tactile. 



As we should expect, the latent period for pain 

 is noticeably longer than the latent period for contact 

 or for heat and cold : we feel the contact and know 

 that the object is very hot or very cold, some con- 

 siderable time before we are conscious that these 

 stimuli are dolorific. 



These two facts then make it clear why fusion 

 of sensations should occur more easily in tactation 

 than in algesia ; faradisation of pain-spots at 20 

 per second gives a continuous painful sensation, 

 while with faradisation of touch-spots at 30 per 

 second the stimuli are still perceived discrete. 



The number of stimuli per second necessary to 

 induce a continuous sensation is evidently inversely 

 as the magnitude of the functional inertia of the 

 sensory apparatus involved, thus, discontinuity is 

 still experienced from a violin-string vibrating 1552 

 times per second, and a toothed wheel does not 

 give a smooth sensation until the teeth meet the 

 skin at between 480 and 640 times per second. 



* C. S. Sherrington in " Text-book of Physiology." Edited by 

 Schafer, vol. ii. p. 925. 



