362 SPECIAL PHYSIOLOGY. 



is, as its name implies, that of contact with some external object, or 

 the touching of matter. By the aid of touch, combined with pressure, or 

 movement, or with both, we arrive, however, at more important results, 

 viz., at compound impressions. For example, from touch and pressure 

 we obtain the feeling of external resistance; and, according to the de- 

 gree of this we acquire a knowledge of the solidity, viscosity, fluidity 

 or aeriform conditions of matter, and thus gain our notions of hardness, 

 softness, elasticity, impenetrability, and so forth. By touch combined 

 with movement we successively arrive at the notions of measure and 

 size, distance and space. By the same means we examine and appre- 

 ciate the forms of bodies; and by the combined operation of touch, 

 pressure, and movement, we learn the characters of surfaces, such as 

 roughness, smoothness, or polish. Finally, by touch co-operating 

 with the muscular sense or the feeling of internal resistance, we are 

 able to appreciate weight. Touch, though the simplest and least spe- 

 cial, is the most general, and, at the same time, the most direct, posi- 

 tive, and certain of the senses. It is the logical as well as the physio- 

 logical parent of the other senses, which are, in the last analysis, 

 modifications of touch. It is the sense the least liable to be deceived. 



The sensations of contact and resistance, and also, it may be added, 

 those of temperature, and of pain or its opposite, are always referred 

 to the parts of the body acted on by the external object; in all cases, 

 but especially in the first three, a certain perception of the regions 

 touched, resisted, or heated, that is, of the locality or seat of the sensory 

 impressions, is superadded ; although, as we know, the actual seat of 

 all sensations is in the part of the great nervous centres, named the 

 sensorium. It is on the more perfect possession of this perception of 

 the locality of impressions of contact, that the specialized form of sen- 

 sation, which constitutes tact or the tactile sense, to a large extent 

 depends. 



All parts of the skin and the adjoining mucous membranes are en- 

 dowed with the sense of contact or touch ; but, in man, it is the hand, 

 which, by common usage and cultivation, is the special organ of the 

 higher tactile sense. It is most admirably fitted for its office, by reason 

 of the number, size, arrangement, structure, and abundant nervous 

 supply of its papillae. The whole mechanism of the upper limb is, 

 indeed, wonderfully adapted for the due fulfilment, not only of the 

 prehensile, but also of the tactile functions of its digital extremities. 

 The numerous articulations of the fingers, the length of the phalanges, 

 the size and strength of the thumb, the power of bringing it into exact 

 opposition with the ends of the fingers, so as to form, with them, as it 

 were, a pair of pincers, enable the hand to span objects in all direc- 

 tions, and to examine their relative consistence, size, and character of 

 surface. The bones and nails serve as firm points of support for the 

 skin, and aid materially in the exercise of the tactile sense, and in its 

 secondary or derived uses. 



Those cutaneous papillae which contain nerves, are the proper or- 

 gans of tactile sensibility, their number, size, arrangement, com- 

 plexity of structure, and nervous supply being, as exemplified in the 

 hands and feet, in exact proportion to the perfection of this sense in 



