PER CEPTION OF RESISTANCE. i o 2 1 



sitive. Cocainisation of the vocal cords does not hamper the manage- 

 ment of the voice. 1 The cocainised eyeballs can be well trained in any 

 desired direction in a perfectly dark room. 2 In tabes dorsalis, in which 

 the chief lesion concerns the afferent roots, locomotor ataxy is a character- 

 istic, and in this disease the early loss of the knee-jerk indicates the 

 early breakdown of the afferent nerve fibres of the muscles of the lower 

 limb. Besides the consequent loss of tension, the loss of what Bastian 

 calls " guiding " sensations is probably a factor in the inco-ordination. 



To the organs of muscular sense is largely traceable local " feel- 

 ing of fatigue." In tabes dorsalis the patient is often abnormally 

 resistant to the induction of this feeling in certain groups of muscles, 

 even on prolonged exercise of them (compare above, pp. 972 and 990). 



Finally, there is the phenomenon of senso-paralysis. Charles Bell 

 noted that after section of the supramaxillary (purely afferent) divisions 

 of both trigemini, power to use the upper lip for prehension (ass) is 

 lost. In the monkey the " grasp " of hand or foot in lost in an 

 apassthetic limb. 3 These instances suffice to indicate that in their 

 relation to afference some movements stand very differently to others. 



Exner finds it impossible, without the help from a retinal image, to at 

 all accurately converge the eyes for an object, which, though unseen, e.g. 

 in a dark room, has its direction and distance well perceived, since it is 

 held before one in one's hand. 



Perception of resistance. — Muscles are physiological machines for 

 antagonising various forces by elastic tension. In so doing, certain 

 changes in consciousness are brought about, and among these is a 

 " sense of resistance." To hold between the fingers a thread that 

 carries a weight, gives a sensation as of the existence outside the fingers 

 of a something only describable as offering resistance. It is, however, 

 difficult to think of " resistance " as a quite elementary sensation. It 

 can perhaps be simplest thought of as sensation of tension ; but dis- 

 crimination between resistances is based on ratios between degrees of 

 tension sensations and other sensations, such as posture, excursion, and 

 speed of movement, and on touch. More accurate judgment of the 

 weight of an object can be found by lifting it than by allowing it simply 

 to rest on the supported hand. Touch is contributory, but the basis of 

 the judgment seems to be those sensations accompanying the muscular 

 action which are called kinesthetic. When the finger presses down the 

 beam of a balance, counterweighted by weights ranging between 200 and 

 2000 grms., a constant fractional increase of about ^ is found to be the 

 liminal sensible difference, if active movement of the finger be not 

 employed, but that fraction falls to T V when the finger is pressed down 

 by willed movement. 4 



Liminal stimulus. — The load affording the limen of sensible resistance for 

 the elevators of the shoulder has been found 5 to be in a given case 7*5 grms., 

 hung at the tip of the forefinger, the arm being horizontal and joint move- 

 ment limited to the shoulder. With movement at the elbow only, the load 

 had to be increased to 9 grms. ; and with movement in the finger only, to 



1 H. Beaunis, Oompt. rend. Soc. d. psychol. physiol., Paris, 1887. 

 - Sherrington, Proc. Roy. Soc. London, 1897, vol. lx. 



3 Mott and Sherrington, ibid., 1895, vol. lvii. ; cf. also Exner, Arch. f. d. gcs. Physiol., 

 Bonn, 1892, Bd. 1. 



4 Merkel, Phil. Stud., Leipzig, Bd. v. S. 287. 



5 Goldscheider and Blecher, Arch. f. Physiol., Leipzig, 1893. 



