066 HANDBOOK or PHYSIOLOGY. 



So, with regard to the ideas derived from sensations of touch com- 

 bined with movements, it is doubtful how far the consciousness of the 

 extent of muscular movement is obtained from sensations in the muscles 

 themselves. The sensation of movement attending the motions of the 

 hand is very slight; and persons who do not know that the action of 

 particular muscles is necessary for the production of given movements, 

 do not suspect that the movement of the fingers, for example, depends 

 on an action in the forearm. The mind has, nevertheless, a very definite 

 knowledge of the changes of position produced by movements; and it 

 is on this that the ideas which it conceives of the extension and form of 

 a body are in great measure founded. 



There is no marked development of common sensibility to be made 

 oat in muscles: they ma}' be cut without the production of pain. On the 

 other hand, there is no doubt that afferent impulses must pass upward 

 from muscles and tendons acquainting the brain with their condition. 

 This, then, must be a special sense. It has been suggested that the minute 

 end-bulbs of Golgi found in tendons, and that the Pacinian corpuscles in 

 the neighborhood of joints, are the terminal organs of this special sense. 



Judgment of the Form and Size of Bodies. By the sense of touch the 

 mind is made acquainted with the size, form, and other external char- 

 acters of bodies. And in order that these characters may be easily 

 ascertained, the sense of touch is especially developed in those parts 

 which can be readily moved over the surface of bodies. Touch, in its 

 more limited sense, or the act of examining a body by the touch, consists 

 merely in a voluntary employment of this sense combined with move- 

 ment, and stands in the same relation to the sense of touch, or common 

 sensibility, generally, as the act of seeking, following, or examining 

 odors, does to the sense of smell. The hand is the best adapted for it, 

 by reason of its peculiarities of structure, namely, its capability of 

 pronation and supination, which enables it, by the movement of rota- 

 tion, to examine the whole circumference of the body; the power it 

 possesses of opposing the thumb to the rest of the hand, and the relative 

 mobility of the fingers; and lastly from the abundance of the sensory 

 terminal organs which it possesses. In forming a conception of the 

 figure and extent of a surface, the mind multiplies the size of the hand 

 or fingers used in the inquiry by the number of times which it is con- 

 tained in the surface traversed; and by repeating this process with 

 regard to the different dimensions of a solid body, acquires a notion of 

 its cubical extent, but, of course, only an imperfect notion, as other 

 senses, e.g. , the sight, are required to make it complete. 



It is impossible in this consideration to say how much of our knowl- 

 edge of the thing touched depends upon pressure and how much upon 

 the muscular sense. 



