100 PHYSIOLOGY CHAP. 



According to Goldscheider, the speed of the movement is 

 important, as well as its amplitude. A movement that was 

 imperceptible but close to the threshold of excitation became 

 appreciable when its velocity was increased. It is possible also 

 to establish numerical relations between the two main factors of 

 the passive movements. The liminal speed, that is the minimal 

 degree of angular movement per second, varies in the different 

 articulations from about '25 to 1'4. 



Goldscheider holds that the perceptions of posture and of 

 passive movement depend fundamentally on the deep sensibility 

 of the articulations. Not only are vision and touch not indis- 

 pensable to them, but the sensibility of the muscles and tendons 

 are of no appreciable importance : the minimal angle of excursion 

 necessary to give the perception of the passive movement remains 

 the same, whatever the initial posture of the articulation. Again, 

 the result does not alter after the skin of the limb has been 

 anaesthetised by electricity : when the cutaneous sense of pressure 

 on the skin is thus eliminated, perception becomes more acute. 

 When, on the other hand, the joints are made insensitive, the 

 perception of movement becomes blunted, and the movements 

 must be of a wider range to be appreciable. 



Hence, according to Goldscheider, the articular surfaces are 

 the exclusive starting-point of the sensations by means of which 

 we directly perceive the passive movements of our limbs. 



Of course the perception of active movements also depends 

 upon the compressions and excursions of the articular surfaces ; 

 but other factors intervene here the tension of the tendons, and 

 probably also the changes in form of the active muscles, besides 

 the passive traction of antagonist tendons and muscles. In fact, 

 according to Goldscheider, the sensibility to active movements is 

 more delicate than to passive movements, although the difference 

 is not very large. 



VII. The discussion of the sensory phenomena connected with 

 active voluntary movements would be inadequate and incomplete 

 if we did not take another important factor into account. Besides 

 the more or less obscurely appreciated sensations which accompany 

 movement, and which are aroused at the periphery by excitation 

 of the terminal sensory organs of the articular tissues, tendons, and 

 muscles which we have considered under the general name of 

 muscular sense, we have to consider the central sensation that 

 precedes the movement, which coincides with the volitional act 

 and gives rise to the efferent current along the motor paths. 

 Johannes Miiller, Helmholtz, Wundt, Bain, to cite only the most 

 eminent authorities, maintain that we have not only a sensation of 

 the movement executed, but also a sensation of the movement 

 willed ; that the sensation of the active movement is directly asso- 

 ciated with motor innervation ; that we perceive the intention 



