PER CEPTION OF POSTURE. 1013 



motor and respiratory, are elicited by intensities of stimulus not beyond the 

 bounds of normal, or exaggerated, so as to be dolorous. To discriminate between 

 the two possibilities, I have stimulated the peripheral ends of the cut motor 

 roots of the nerves of the hamstring muscles (cat), the afferent roots remain- 

 ing intact. It is then found that even when the anaesthesia is shallow the 

 muscles can be thrown into a very vigorous and complete tetanic contraction, 

 maintained even for 30 seconds, or more, without producing noticeable effect 

 on the general arterial blood pressure or on respiratory rhythm. When the 

 stimulation is increased sufficiently, and the contraction is therefore very severe, 

 slight effects on blood pressure and respiration are obtainable, but the attendant 

 risk of some escape of the stimulating current to the sensory roots is not 

 entirely excluded. 



From the point of view of muscular sense proper, more interesting than 

 the reflex effects upon vasomotor and respiratory mechanisms, are those upon 

 the local musculature. These latter exemplify certain degrees of co-ordination, 

 including "reciprocal innervation." From skin and the cutaneous nerves 

 similar reflexes can be excited, although it would seem less readily. 



The Performances of Muscular Sense. 



The perceptions of muscular sense may be grouped into (i.) those of 

 posture, (ii.) of passive movement, (iii.) of active movement, and (iv.) those 

 of resistance to movement. Changes in consciousness accompany all 

 movements of the body which occur at speeds above a certain liminal, 

 and over distances of beyond a certain liminal extent. Most move- 

 ments of the body alter the position of one part of it relatively to 

 another, as well as alter the body's position relatively to its environ- 

 ment, without altering the mutual space-relationship between different 

 parts of the body. The latter class may, from the physiological point 

 of view, be termed " solely extra-relative." All these kinds of move- 

 ments are perceptible by the mind, in virtue of the space perceptions 

 with which it is furnished, by the combined labours of the senses of 

 sight, touch, and the organs of the labyrinthine and muscular senses. 

 But with solely extra-relative movements the muscular sense is usually 

 little concerned, and consideration of them can be omitted from any 

 brief exposition of " muscular sense." 



Perception of posture. — This is not the place to discuss how the 

 position of the body, considered as a whole, in reference to the earth's 

 centre, and contradistinguished from all else which is " environment," 

 is perceived. For that, much else besides the muscular sense is in- 

 strumental. To that, the muscular sense contributes limited perceptions 

 of the relative positions of the corporeal parts, e.g. of the limbs, their 

 joints, etc. The muscular sense is no doubt a large contributor toward 

 the perception of the mechanical equilibrium of the body, and in that 

 way toward the regulation and maintenance of its stability. The 

 necessary corrective movements that, during locomotion, prevent gravity 

 pulling us prone, or as we sit, stand, or maintain postures natural to 

 us (our usustatus, ususihis, usumotus), involve perceptions of the relative 

 position of our corporeal parts are guided by — one might almost 

 say supplied by — the muscular sense. These perceptions, though not 

 for the most part " objects " of attention, determine actions, and can 

 be attended to at once, should need arise. That in the dark one hand, 

 passively placed, can be touched on any desired finger-tip by a finger 

 of the other hand, illustrates our possession of a sense of posture largely 



