102 PHYSIOLOGY CHAP. 



may be vague or disappear it is readily called up again by any 

 influence affecting the stump (Vol. III. p. 201). Weir-Mitchell 

 shows that the illusion of the presence of the lost limb is per- 

 sistent, and may be so vivid that some persons who have under- 

 gone amputation are more certain of the existence of the missing 

 than of the remaining limb. That sensation rarely extends, how- 

 ever, to the whole limb. In a third of the cases of amputation 

 through the thigh, and half the cases with amputated arms, there 

 is a feeling that the missing foot or hand is nearer the trunk than 

 in the corresponding intact limb. The most interesting point for 

 the argument is that there are subjective sensations of movement 

 in the amputated limbs. The patient is nearly always capable of 

 voluntary change in the phantom of the missing limb, and can 

 produce sensations of flexion and extension, if not of the whole of 

 the joints, at least of the fingers or toes of the missing limb. 

 Generally speaking, these voluntary efforts are injurious and 

 produce itching at the stump; but in some cases the patient 

 imagines complete freedom of movement in the missing hand, and 

 says, " My hand is open, my hand is closed, now I am touching the 

 thumb with the little finger, now my hand is in the position for 

 writing," and so on. From these and other interesting phenomena 

 which he describes in detail, Weir-Mitchell concludes that the will 

 to move and the consciousness of movement are synchronous, 

 and occur simultaneously in the centres. At each volition the 

 consciousness of the act to be performed, with its qualities, surges 

 up in the mind. These phenomena are erroneously attributed 

 to impressions coming from the periphery. 



(d) Z. Treves assumes the existence of a sense of innervation, 

 by which we have a direct appreciation of centrifugal impulses 

 sent out by the motor centres, because we habitually regulate the 

 volitional impulse in such a way that the external change effected 

 by the muscles brings about the desired effect, both in amplitude 

 and speed, with the least expenditure of energy on the part of 

 the muscles, independently of sensations conveyed from the peri- 

 phery by the muscular sense. 



A proof that this regulation of the volitional impulse really 

 exists and is central in origin is given by the experiment of the 

 bottle (quoted by Johannes Miiller in his Text-book), in which if an 

 empty bottle which the subject believes to be filled with a more or 

 less heavy fluid is raised, it acquires unexpected velocity, and almost 

 precedes the movement of the arm it flies, in Fechner's picturesque 

 expression. This excess of energy expended when the subject 

 does not know if it is full or empty would not appear if the 

 intensity of the centrifugal impulse depended solely on the peri- 

 pheral sensations due to muscular activity. 



In analogy with this are the phenomena described by G. E. 

 Miiller and Schumann relative to certain errors in the estimation 



