16 SPECIAL SENSES. 



characteristic phenomena is inability to stand when blind- 

 folded ; although, with the aid of the sight, the muscles can 

 be made by the will to act with great power. 



Without entering into a full discussion of the various ar- 

 guments used for and against the existence of a special 

 "muscular sense," it is sufficient to state that, in those cases 

 in which general sensibility is lost or seriously impaired, the 

 brain has no exact appreciation of the action of the muscles, 

 except as regards the sense of fatigue. This question is of 

 great importance in connection with the pathology of the 

 nervous system ; and it seems that the weight of evidence is 

 decidedly in favor of the view, that there is no distinct per- 

 ception of muscular action, aside from general sensibility, 

 that can properly be called a muscular sense. 



Habit and education enable us to appreciate with great 

 nicety differences in weight ; but this is chiefly due to the 

 sense of resistance to muscular effort, and has little depend- 

 ence upon the sense of touch. In the elaborate and clas- 

 sical experiments of Weber, this point was very strikingly 

 illustrated. The observations of this. physiologist upon the 

 sense of touch and general sensibility were very varied and 

 extensive ; and, among the most important of the results with 

 regard to the appreciation of pressure and weight, are the 

 following : 1 



In general, those parts which are most sensitive to the 

 impressions of touch, as the fingers, enable us to appreciate 

 differences in pressure and weight with the greatest accuracy. 

 The sense of simple pressure, unaided by the estimation of 

 weight by muscular effort, is generally more acute upon the 

 left side, probably because the integument of the left hand is 

 thinner than that of the right hand. Differences in weight 

 can be accurately distinguished, when they amount to only 

 one-sixteenth, by employing muscular effort in lifting, as 

 well as the sense of pressure ; but the sense of pressure alone 



1 WEBER, Drucksinn, in WAGNER, ffandworterbuch der Physiologic, Braun- 

 schweig, 1846, Bd. iii., zweite Abtheilung, S. 543, et seq. 



