WILL. 607 



innervation regard them as experimenta crucis. Helmlioltz 

 writes : * 



" When tlie external rectus muscle of the right eye, or its nerve, is 

 paralyzed, the eye can no longer be rotated to the right side. So long 

 as the patient turns it only to the nasal side it makes regular move- 

 ments, and he pereeiv^es correctly the position of objects in the visual 

 field. So soon, however, as he tries to rotate it outwardly, i.e., towards 

 the right, it ceases to obey his will, stands motionless in the middle of 

 its course, and the objects appear flying to the right, although position 

 of eye and retinal image are unaltered. t 



" In such a case the exertion of the will is followed neither by actual 

 movement of the eye, nor by contraction of the muscle in question, 

 nor even by increased tension in it. The act of wiW produced ahsolutely 

 no effect beyond the nervous system, and yet we judge of the direction 

 of the line of vision as if the will had exercised its normal effects. We 

 believe it to have moved to the right, and since the retinal image is 

 unchanged, we attribute to the object the same movement we have er- 

 roneously ascribed to the eye. . . . These phenomena leave no room 

 for doubt that we only judge the direction of the line of sight by the 

 effort of will with which we strive to change the position of our eyes. 

 There are also certain weak feelings in our eyelids, . . . and further- 

 more in excessive lateral rotations we feel a fatiguing strain in the 

 muscles. But all these feelings are too faint and vague to be of use in 

 the perception of direction. We feel then what impulse of the will, and 

 how strong a one, we apply to turn our eye into a given position." 



Partial paralysis of the same muscle, paresis, as it has 

 been called, seems to point even more conclusively to the 

 same inference, that the will to innervate is felt independ- 

 ently of all its afferent results. I will quote the account 

 given by a recent authority, % of the effects of this accident : 



"When the nerve going to an eye muscle, e.g., the external rectus 

 of one side, falls into a state of paresis, the first result is that the same 

 volitional stimulus, which under normal circumstances would have per- 

 haps rotated the eye to its extreme position outwards, now is competent 

 to effect only a moderate outward rotation, say of 20°. If now, shutting 

 the sound eye, the patient looks at an object situated just so far out- 



* Pbysiologische Optik, p. 600. 



f [The left and sound eye is here supposed covered. If both eyes look 

 at the same field there are double images which still more perplex the judg- 

 ment. The patient, however, learns to see correctly before many days or 

 weeks are over. — W. J.] 



t Alfred Graefe, in Handbuch der gesammten Augenheilkunde, Bd. 

 VI. pp. 18-21. 



