ioi8 THE MUSCULAR SENSE. 



outlines are drawn fairly equal. If, then, the attempt be repeated but with the 

 starting-point B considerably above A, the ascending part of the outline of the 

 right-hand figure is smaller than the corresponding of the left-hand figure ; 

 the descending part, on the contrary, is longer. 



Symmetrical muscular movements executed with the intent to be, 

 and after performance judged to be, equal, show habitual preponderance 

 of one side, right or left, in different persons (Stanley Hall), and this 

 without dependence on right-handedness or left-handedness, 1 but rather 

 upon muscular development due to influence of occupation. Bloch, 

 however, states that, in measuring the number of pages of a book 

 between the finger and thumb, the distance is under-estimated by the 

 left hand with right-handed people, but by the right hand with left- 

 handed people. 



It seems that speed of movement is not very correctly judged. In 

 the above-mentioned illusions the total duration of the movement is 

 equal, and the speed of movement is not detected to be different. Loeb 

 found that the weighting of a hand — thereby introducing a resist- 

 ance — did not much affect the result. He concluded from this that 

 mere tension of muscle was not a chief basis for the sensation. Exner's 

 illusion 2 points in the same direction. If a plate of vulcanite be placed 

 between the teeth and bitten upon, the sensation given is as though the 

 jaws moved perceptibly toward one another, although the plate be really 

 quite unyielding ; the illusion is obtained of the teeth sinking slightly 

 into the substance bitten. Sternberg's illusion 3 mentioned above is 

 comparable with these. 



Objective Effects of Loss of Muscular Sense upon 

 " Willed " Movements. 



The office of the muscular sense in regard to willed movement can 

 also be studied to a certain and fortunate degree objectively. It is 

 found that the destruction of sensitivity in particular regions brings 

 about objectively observable disturbances of movement. A region 

 totally deprived of sensation by section of its afferent nerves, is termed 

 apcesthetic, and the effects of apa^sthesia upon the musculature of 

 the part are three — (1) paralysis, (2) ataxia, (3) atonia. Certain 

 elementary adjustments of muscular action occur reflexly without 

 awakening attention or in the slightest degree seeming to trouble at 

 all the stream of consciousness. Yet these have, inf eriorly and remotely, 

 relationship to the highest achievements of the muscular sense, such 

 as the manipulative finesse of the human thumb and finger. The 

 muscular sense embraces the part played by sources of afterence in 

 the taxis of muscular activity, even where the reactions lie not amen- 

 able to introspection. The physiologist derives a certain advantage 

 from this, in that it offers an objective mode of studying the activities 

 of the afferent apparatus of muscular sense by watching the objective 

 effects of it on the characters of muscular movements. 



The unconscious reflex actions of the adult may be taken to represent 

 those reactions accruing to him phylogenetically or ontogenetically, 

 which, though of ancient origin, have with little metamorphosis remained 

 on the average useful to him as an adult member of his species. As to 



1 M. Cremer, "Inaug. Diss.," Wiirzburg, 1887. 



2 See Sternberg, Arch. f. d. yes. Physiol., Bonn, 1895, Btl. lix. 3 Ibid. 



