818 FEELING AND TOUCH. 



and the ulriar side of the ring finger to bear at the same time on a small 

 object, such as a marble. Hence, when with the eyes shut we cross one 

 finger over the other, and place a marble between them so that it touches 

 the radial side of the one and the ulnar side of the other, we recognize that 

 the object is such as could not under ordinary conditions be touched at the 

 same time by these two portions of our skin, and therefore judge that we 

 are touching not one but two marbles. Upon repetition, however, we are 

 able to correct our judgment, and the illusion disappears. 



750. Distinct tactile sensations are, as we have seen, produced only 

 when a stimulus is applied to a terminal organ. When sensations or affect- 

 ions of general sensibility other than the distinct tactile sensations are 

 developed in the termination of a nerve, we are still able, though with less 

 exactitude, to refer the sensation to a particular part of the body. Thus, 

 when we are pricked or burned, we can feel where the prick or burn is. 

 When a sensory nerve-trunk is stimulated, the sensation is always referred 

 to the peripheral terminations of the nerve. Thus a blow on the ulnar nerve 

 at the elbow is felt as a tingling in the little and ring fingers corresponding 

 to the distribution of the nerve, and sensations started in the stump of an 

 amputated limb are referred to the absent member. When cold is applied 

 to the elbow it is felt as cold in the skin of the elbow ; but a cooling of the 

 ulnar nerve at this spot, since stimulation of a nerve-trunk gives rise to 

 general sensations only, simply gives rise to pain which is referred to the 

 ulnar side of the hand and arm. 



THE MUSCULAR SENSE. 



751. When we come into contact with external bodies we are con- 

 scious not only of the pressure exerted by the object on our skin, but also of 

 the pressure which we exert on the object. If we place the hand and arm 

 flat on a table, we can estimate the pressure exerted by bodies resting on the 

 palm of the hand, and so come to a conclusion as to their weights ; in this 

 case we are conscious only of the pressure exerted by the body on our skin. 

 If, however, we hold the body in the hand, we not only feel the pressure of 

 the body, but we are also aware of the muscular exertion required to sup- 

 port and lift it. We possess a muscular sense ; and we find by experience 

 that when we trust to this muscular sense as well as to sensations of pres- 

 sure, we can form much more accurate judgments concerning the weight of 

 bodies than when we rely on sensations of pressure alone. When we want 

 to tell how heavy a body is, we are not in the habit of allowing it simply to 

 press on the hand laid flat on a table ; we hold it in our hand and lift it up 

 and down. We appeal to our muscular sense to inform us of the amount 

 of exertion necessary to move it, and by help of that, judge of its weight. 

 And in all the movements of our body we are guided, even to an astonish- 

 ing degree of accuracy, as is well seen in the discussions concerning vision, 

 by an appreciation, more or less distinctly conscious, of the amount of the 

 contraction to which we are putting our muscles. In some way or other we 

 are made aware of what particular muscles or groups of muscles are being 

 thrown into action, and to what extent that action is being carried. We are 

 also conscious of the varying condition of our muscles, even when they are 

 at rest ; the tired and especially the paralyzed limb is said to " feel" heavy. 

 In this way the state of our muscles largely determines our general feeling 

 of health and vigor, of weariness, ill health and feebleness. 



It has been suggested that since muscle possesses little or no general 

 sensibility, comparatively little pain being felt for instance when muscles are 

 cut, our muscular sense is chiefly derived from the traction of the contract- 



