ii SKXSIBILITY OF THE INTERNAL OKCANS 101 



before the fact; that the idea of the contraction precedes ;md does 

 not follow the nio\einent. 



lint this theory of a central sense of innervation, as opposed to 

 that of the peripheral muscular sense, finds no supporters in view 

 of the progress and development of the theory discussed above. 

 Some physiologists still maintain that in all voluntary acts a. 

 central feeling of innervation is associated with the multiple 

 peripheral sensations; the majority, however, deny Bain's theory 

 even in this restricted form, and maintain that the sense of effort 

 results exclusively from a consensus of afferent elementary sensa- 

 tions. We must weigh the arguments for and against the two 

 theories before deciding in favour of one or the other : - 



() Certain phenomena observed on paralysed patients were 

 formerly adduced in favour of the central sense of innervation. 

 If a paralysed person is invited to make a movement with his 

 paralysed limb he puts out all his force without success, and is 

 fully conscious of the effort he makes, although this cannot depend 

 on any excitation from the peripheral organs of the paralysed 

 limb. But it is obvious that this and other similar arguments 

 adduced in support of the theory of an innervating sense are of 

 little value. It has in fact been pointed out by Vulpian and 

 others that when the paralysed person attempts to move the 

 paralysed limb, he throws into action a number of non-paralysed 

 muscles in other regions, and the sensation of effort felt may be 

 due to the movements performed by these muscles. 



(J) If the sensation that accompanies the movement were due 

 solely to peripheral excitations, there would, according to Wundt, 

 be perfect parallelism between the sensation and the muscular 

 contraction. But, as a matter of fact, we know by experience that 

 the sensation does not depend principally on the extent of the 

 movement effectively carried out, but on the force of the impulse 

 that emanates from the motor centre. In proof of this we may 

 cite the fact described by Delboeuf. If any one repeatedly exerts 

 the whole force of his hand on a spring dynameter, he has the 

 illusory sensation of using the same effort each time, and is 

 surprised to see the rapidly decreasing values in a series of ten or 

 twelve efforts. There is evidently no parallelism here between 

 the sensation of effort, which remains uniform, and the movement 

 actually carried out, which rapidly decreases. So that we may 

 conclude that the first is central in origin and does not depend on 

 the second. 



(c) Weir-Mitchell argued in favour of a central sense of inner- 

 vation from the illusory phenomena observed after amputations, of 

 which he made an exhaustive study from over 100 patients. It 

 has been known since the time of Johannes Miiller that nearly all 

 persons whose limbs have been amputated (94 in 100) have the 

 illusion that the lost limb is still in its place, and though this feeling 



