ii SENSIBILITY OF THE INTEKNAL OKGANS 107 



with which it is connected are nearly always intimately connected 

 with the central and peripheral sensations that coincide with 

 voluntary acts. In the same way the preceding remarks on the 

 muscular and innervation senses do not sufficiently emphasise 

 their psychological importance, because in analysing our per- 

 ceptions of movement we cannot separate them from the tactile 

 sensations with which they are nearly always accompanied 

 in life. 



Bernstein rightly distinguishes between passive and active 

 tactile sensibility: the former comes into play when a body is 

 brought into contact with, or exerts pressure on, the immobile 

 cutaneous surface, e.g. on applying the two points of Weber's 

 compasses to the skin ; the latter when we pass the hand or 

 fingers to and fro over the surface of a body, and move or lift it, 

 so as to discern its form, size, resistance, weight, and other 

 accessory physical characters. This last is the usual application 

 of the tactile sense ; but it is plain that in using active touch, 

 and in touching objects, the tactile sensations must be combined 

 with muscular sensations or the sense of movement. Now that 

 we have analysed these sensations separately it will be well to 

 put them together and compare them, the better to understand 

 their nature and relative physiological and psychological im- 

 portance. 



We have seen that we possess the capacity of localising tactile 

 sensations more or less precisely at different points of the skin, 

 according to the relative number of the touch spots and the 

 higher or lower threshold of excitability in the different regions. 

 Muscular sensations, on the contrary, are very vaguely localised^ 

 Generally speaking, we do not feel the contraction of the muscles, 

 which are the active organs of movement, but only the movement 

 or displacement of the limb. It is only on focussing our attention 

 sharply that we succeed in vaguely localising sensation in the 

 joint, or the muscle or group of muscles, that is contracting. 

 Normally we localise the muscular sensation according to the 

 signals received at the same time through the senses of touch and 

 vision; and when these are excluded we localise the motor 

 sensations according to the mnemonic signs which we possess of 

 the visual and tactile sensations by which they are usually 

 accompanied. If, for instance, with the eyes closed we trace 

 figures in the air with the extended forefinger, we are as plainly 

 aware of the tracings described by the end of the finger as if we . 

 saw them with our eyes, while in reality the surface of the finger- 

 tip receives no impression. The physiological basis of this 

 percept is certainly formed by the central impulses and simul- 

 taneous muscular contractions of the limb which displace the 

 joints in various ways, and must vary with the variation of the 

 angles, straight lines, or curves that we trace in the air with the 



