TOUCH 237 



B. Chemical Energy. 



The various chemical stiumli to which the organism is exposed 

 have receptors in the skin, giving rise to sensations of pain or 

 discomfort, and in the special end-organs to those of taste and 

 smell. 



As receptors for tliese various manifestations of energy we 

 have the so-called five senses. That is, five different means are 

 employed for the purpose of orientation, viz. touch, hearing, 

 sight, smell and taste. These senses come into contact with the 

 external forces through the skin, ear, eye, nose and tongue. 

 But some of these are composite end-organs. The skin, for 

 instance, includes not only touch corpuscles but the end-organs 

 for pain and temperature. The ear not only analyses sounds, but 

 contains organs for the static and dynamic senses. In all there 

 are over twenty different kinds of receptors and sense-organs in 

 the bodv. 



I. PHASIC RECEPTORS 



1. Touch is the sense by which mechanical force is appreciated. 

 Mere contact is gentle pressure, a greater amount of applied force 

 causes a feeling of resistance referred to the skin, a still greater 

 amount evokes a response from receptors in the muscle, while 

 pain results from great pressure. The total number of tactile 

 corpuscles (excluding those on the head) has bieen estimated as 

 500,000. These are not evenly distributed over the skin, but are 

 more numerous and more sensitive on certain of the more mobile 

 parts of the body, e.g. tongue and fingers. The degree of sensitive- 

 ness of the skin may be determined by some form of aesthesiometer 

 (say a pair of compasses) by means of which one may measure 

 the smallest distance at which impress of the two points may be 

 perceived as two distinct sensations. The following table gives 

 the activity of the discriminating sense for different parts of the 

 skin : 



TABLE XXXIII. 



Tip of the tongue .... 

 Third phalanx of finger, volar surface . 

 Red part of the lip . 

 Second phalanx of finger, volar surface 

 First phalanx of finger, volar surface . 

 Third phalanx of finger, dorsal surface 

 Tip of nose ..... 

 Head of metacarpal bone, volar surface 

 Ball of thumb ..... 

 Ball of little finger .... 



Millimetres. 



11 

 2-2-3 



4-5 

 4-4-5 

 5-5-5 



6-8 



6-8 

 5-6-8 

 5-7-6 

 5-5-6 



