1428 ON CUTANEOUS AND [BOOK in. 



other hand with fibres of common sensibility having no such specific 

 terminal organs, the two kinds of fibres being mixed together in 

 the common cutaneous nerve. These fibres moreover have not 

 only different peripheral but also different central endings, and 

 during at least some part of their course run in different tracts 

 or in a different manner in the central nervous system ; for as we 

 saw in treating of the central nervous system ( 683) cases of 

 disease of the central nervous system have been recorded in winch 

 over certain cutaneous areas sensations of touch had been lost, 

 while common sensibility and sensations of pain remained, or vice 

 versa. We may add that the difference between the central paths 

 or endings of the nerves of touch and those of pain is further 

 shewn by the fact that in certain nervous diseases (tabes) when the 

 skin is pricked with a pin, the contact of the pin may be felt as 

 mere touch for so long a time as one or two seconds before pain 

 is felt ; the diseased condition enormously delays the transmission 

 of the impulses of pain but has not so much effect on those of 

 touch. 



887. We may go a step further ; there is a certain amount 

 of evidence that the terminal organs and fibres concerned in touch 

 proper, in sensations of pressure, are different and separate from 

 those concerned in sensations of heat and cold. In the first place 

 the general topographical distribution over the surface of the body 

 of sensitiveness to pressure is different from that of sensitiveness 

 to temperature. A familiar instance of this is seen in bringing 

 the palm of the hand to touch the forehead. In the former the 

 sense of touch is highly developed, in the latter the sense of tem- 

 perature ; hence with the forehead we feel that the hand is warm 

 or cold, with the hand we feel that the forehead is rough or smooth ; 

 at least these two feelings respectively preponderate, the one in 

 the one part, the other in the other. In the second place cases of 

 disease of the central nervous system of the spinal cord have been 

 recorded in which, over certain cutaneous areas, sensations of 

 pressure were lost but sensations of temperature remained, and 

 vice versa. In the third place, if the stimulation of the skin be 

 confined to extremely minute areas, if the pressure, or the change 

 of temperature be brought to bear as much as possible on a mere 

 point of the skin, it is found that some points of the skin are 

 sensitive to pressure but not to change of temperature, while 

 others again are sensitive to change of temperature but not to 

 pressure. If a blunt pointed but otherwise fine needle be used to 

 exert pressure, a little exploration will ascertain that at some 

 points the amount of pressure can readily be recognized, the sense' 

 of touch is acute, while at other points, and these may be quite 

 near the others, the amount of pressure cannot be recognized, and 

 indeed no sensation is experienced until the pressure is excessive 

 and then the sensation felt is not one of touch proper but of pain. 

 Similarly if heat or cold be applied by means of a metal tube or 



