Ji SENSIBILITY OF TIIK INTERNAL OliCANS Id!) 



the tongue, the red edges of I he lips, and the ends of the lingers 

 (see p. 42). Tliis dominant development <>f tactility in the tongue 

 anil lips is satisfactorily explained it' we admit that the muscular 

 sensations reinforce the po\\er of cutaneous localisation by the 

 fact that amongst the earliest, most important, and most eager 

 movements of the new-horn is that of sucking, which is evoked 

 hy an instinctive, central impulse, and is accompanied arid regulated 

 hy the sensations derived from the activity of the lingual and 

 lahial muscles. The great delicacy of tactile sensihility in the 

 linker-tips and palms of the hand, again, is due to the fact that 

 it is hy exercising the active touch of the hand, accompanied hy 

 various movements of the limhs, that the infant seeks and finds 

 the hreast of its nurse, that the growing child gathers its first 

 experiences from its own hody or from external ohjccts, that the 

 adult, lastly, accomplishes the many actions that enahle him to 

 carry on different manual trades. 



The development of muscle sensihility and the corresponding 

 improvement in cutaneous localisation take place very slowly in 

 children, judging from the difficulty with which they learn to 

 touch ohjects, direct their hands to a given spot, make their first 

 steps, and so on. 



In adults, according to Goldscheider's data, the muscular sense 

 reaches a high degree of delicacy owing to the sensibility of the 

 joints. Ami yet when a person with closed eyes is made to 

 imitate with one arm movements that have previously been 

 carried out with the other, the range of the movement being the 

 same but its direction altered, or when the conditions of experi- 

 ment are otherwise changed, there are marked discrepancies 

 between the movement the subject believes himself to be making 

 and that really carried out. This does not agree with the delicacy 

 of discrimination between active and passive movements described 

 by Goldscheider. 



Other experiments of Beaunis and Stanley Hall demonstrate 

 the normal imperfection of the muscular sense when it acts alone 

 in controlling the direction, range, and rate of a movement. Two 

 symmetrical movements carried out with the two upper limbs, 

 with every intention of making them equal, invariably show a 

 preponderance to right or left according to the idiosyncrasy of the 

 subject, quite apart from right- or left-handedness. 



When a thread carrying a weight is supported by the finger, 

 there is a sensation of something external to the finger which 

 offers resistance, but this is obviously not an elementary sensation 

 but a resultant of various factors. The discrimination of different 

 weights was proved by Hering to rest on the comparison of differ- 

 ent elementary sensations of tension, position, excursion, and rate 

 of movement in addition to tactile sensibility. This is why 

 weights are better appreciated when they are raised than when 



