THE RECEPTOR SYSTEM 173 



the sensory nerves of the different organs. Moreover, when we 

 push against an object, or lift it, we are able to form a judgment 

 as to the amount of effort exerted; but here again pressure on 

 skin and joints and tension of tendons come in. Although under 

 normal circumstances the skin sensations are undoubtedly of im- 

 portance, they are not necessary : persons with cutaneous paralysis 

 can, apart from sight, judge truly the position of a limb and the 

 extent of movement made by it; and in many movements change 

 in joint pressure must be very little if any. We have then to look 

 to muscles and tendons themselves for an important part of the 

 sensations, and in both muscles and tendons there are organs in 

 connection with nerve-fibers which are certainly sensory in nature : 

 moreover, muscle sensory nerves appear to be excited by mere 

 passive change of form in the muscle; with the eyes closed each of 

 us can tell how much another person has lifted one of our arms. 



The sensations by which we judge the extent of a muscular 

 movement enable us to determine very minute differences of con- 

 traction; the ocular determination of the distance of an object not 

 too far off to have its absolute distance determined with con- 

 siderable accuracy, depends almost entirely upon judgments based 

 upon very small changes in the degree of contraction of the internal 

 and external straight (recti) muscles, converging or diverging the 

 eyeballs. A singer, too, must be able to judge with great minute- 

 ness the degree of contraction of the small muscles of the larynx 

 necessary to produce a certain tension of the vocal cords. It may 

 be well to point out that we do not refer a muscular sensation to 

 any given muscle or muscles ; it is merely associated with a certain 

 movement or position, and a person who knows nothing about his 

 ocular muscles can judge distance through sensations derived from 

 them, quite as well as any anatomist. This fact is of course cor- 

 related with the fact that in voluntary movement we do not make 

 a conscious effort to contract any particular muscles: the higher 

 nerve-centers are merely concerned with the initiation of a given 

 movement of a given extent, and all the details are carried out by 

 lower coordinating centers. In ordinary daily life in fact we have 

 no interest whatever in a muscular contraction per se; all we are 

 concerned with is the result, and consciousness has never had need 

 to trouble itself, if it could, with associating a particular feeling or 

 a particular movement with any individual muscle. 



