I024 THE MUSCULAR SENSE. 



and on seven occasions the heavier. A weight, 876 grms., compared with that 

 of 626 grms., was on all of ten occasions judged the heavier. The " standard " 

 weight, 626 grms., and a weight of 2476 grms., were then lifted alternately, 

 each of them thirty times, the "standard" weight preceding the heavier 

 weight. The "standard" was then thrice lifted alternately with weights 926 

 arms. 876 <n-ms., 826 grms. Then the standard was lifted ten times alter- 

 nating with the weight 2476 grms. ; and finally, thrice in alternation with 

 weights 926, 876, and 826. The ten alternatives with the 2476 weight, and 

 the°three with the 926, 876, and 826, were then once more gone through. In 

 the latter part of the experiment the weight 876 grms. was thrice judged to 

 be lighter than 626 grms., and seven times to be equal with it; and weight 

 926 grms. was on nine occasions judged equal to weight 626 grms., and once 

 judged to be lighter than it. This phenomenon is an example of what is 

 termed "adaptation" or "adjustment." 



The motor innervation having become " adapted " for a heavier weight, the 

 perceptions obtained from the peripherally arising impressions resemble in 

 judgment such as would arise under usual circumstances, were a lighter 

 weight than that actually raised to be the object of a smaller effort. Under 

 the more intense motor innervation the weight is actually lifted as quickly as 

 a lighter weight would be were the motor innervation less intense. 



Hering 1 has pointed out how manifold must be the sensations on which 

 estimation of lifted weights is built. Comparisons of perceptions of the speed 

 with which the lifted weights are moved, of the fields of muscular action 

 invoked to maintain the balance of the body as the weight is moved, as well 

 as of skin sensations of pressure and pull, all play a part. A light weight taken 

 up in expectation of its being a heavy one seems to " fly up." An onlooker can 

 often, by watching the speed of lift, tell whether the weight under trial is lighter 

 or heavier than the "standard." Indeed, discrimination between the weights, 

 by lifting them, may be less a matter of discrimination between kinesthetic 

 sensations of tension than between kinesthetic sensations of movement- 

 speeds. 2 But Loeb's experiments (above-mentioned) show that discrimination 

 of speed of willed movement is poor. Movement as such is perceived by the 

 muscular sense. A further datum has been insisted on by Jacobi, namely, 

 the latent period of the movement ; that is, the length of interval between 

 the signal for willing of the movement and the commencement of the 

 movement which is willed. For a given weight a definite latency corresponds 

 with a definite innervation force, and with equal efforts the latency is pro- 

 portional to the amount of the weight. Again, the momentum of the mass 

 moved, and the facility with which the initiated movement can be arrested, 

 may also be a factor in forming the judgment, and will vary with the load 

 lifted. A term "sense of tension" may have to replace "sense of resistance." 

 Of observations on sensible muscle-tensions few exist. Sense of resistance to 

 muscular action may be based on compared sensations of joint movements 

 and of changes of muscle-tension, with or without comparison with sensations 

 signifying changes of muscle form. In these ways may be obtained the 

 distinct perceptions Ave have of the different ways — with ease, or against 

 difficulty — in which the same posture is maintained, or movements identical 

 as regards excursion and velocity are executed. 



Fusion of Muscular Sensations with other Sensations. 



The perceptions furnished by the muscular sense deal largely with 

 the mutual relations between motile parts. By collaboration of muscular 

 sense with certain other senses (especially sight and touch), those 



1 In a letter to Feclmer. 



'-<:. E. M tiller and Schumann, Arch. f. d. gcs. Physiol., Bonn, 1889, Bd. xlv. ; Sunkel, 

 "Inaug. Diss., Marburg," 1890. 



