THE SENSE OF PRESSURE. 543 



get an area of a somewhat circular form, for which the name 

 sensory circle has been proposed. It would be very convenient to 

 explain this on the simple anatomical basis that the impressions 

 of this area were carried by one nerve fibre to the brain, and thus 

 but the one sensation could be produced in the sensorium. But 

 we know this caunot be the true explanation, because of the fol- 

 lowing facts : 1. No such anatomical relationship is known to 

 exist. 2. By practice we can reduce the area of our sensory 

 circles in a manner that could not be explained by the develop- 

 ment of new nerve fibres. 3. If the two points of the compass be 

 placed near the edges of two well-determined neighboring sensory 

 circles, and so in relation with the terminals of two nerve fibres, 

 they will not give distinct impressions ; in fact, they require to be 

 separated just as far as if they were applied within the boundary 

 of one of the circles where they also give rise to the double per- 

 ception. 



To explain better the sense of locality it has been supposed 

 that sensory circles are made up of numerous small areas, forming 

 a fine mosaic of touch fields, each of which is supplied by one 

 nerve fibre, and that a certain number of these little fields must 

 intervene between the stimulating points of the compasses in 

 order that the sensorium be able to recognize the two impulses as 

 distinct. For, although every touch field is supplied by a sep- 

 arate nerve fibril which carries its impulses to the brain, and is 

 therefore quite sensitive, the arrangements in the sensorium are 

 such that the stimuli carried from two adjoining touch fields are 

 confused into one sensation. Thus, when an edge is placed on 

 our skin, we do not feel a series of points corresponding to the 

 individual fields with which it comes in contact, but the confu- 

 sion of the stimuli gives rise to an uninterrupted sensation, and 

 we have a right perception of the object touched. 



THE SENSE OF PRESSURE. 



There seems to be a reason for separating the perception of 

 differences in the degree of pressure exercised by a body from the 

 simple tactile or local impression. If we support a part of the 

 body so that no muscular effort be called into play in the support 



