TASTE AND SMELL 689 



Touch Sensations and 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 characters 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 

 movement, and stands in the same relation to the sense of touch, or com- 

 mon 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 

 teason of its peculiarities of structure namely, its capability of pronation 

 and supination, which enables it, by the movement of rotation, to examine 

 rhe whole circumference of a body; the power it possesses of opposing the 

 thumb to the rest of the hand, and the relative mobility of the ringers; 

 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 contained 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 imper- 

 fect 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 knowledge 

 of the thing touched depends upon pressure and how much upon the mus- 

 cular sense. 



II. TASTE AND SMELL. 



The special sense organs for taste and smell are stimulated by chemical 

 substances, the former by chemicals in solution, the latter by volatile materials. 

 They are also closely associated in action and we do not always differentiate 

 between the two. 



THE SENSE OF TASTE. 



The conditions for the perceptions of taste are: i, the presence of a sense 

 organ, a nerve, and a nerve center with special endowments; 2, the excitation 

 of the sense organ by the sapid matters, which for this purpose must be in a 

 state of solution; 3, a temperature of about 37 to 40 C. (98 to 100 F.). 



The Nerves and Organs of Taste. The principal organ of the sense 

 of taste is the tongue. But the soft palate and its arches, the uvula, tonsils, 

 and probably the upper part of the pharynx, are also endowed with taste. 

 These parts, together with the base and posterior parts of the tongue, are 

 supplied with branches of the glosso-pharyngeal nerve, and evidence has 



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