8 TEXT-BOOK OF PHYSIOLOGY 



Aellum is conjectural. Their ever-present influence is shown by the effect 

 7which follow their removal, as the following facts indicate. 



The prevention of the development of tactile impulses by freezing q 

 anesthetizing the soles of the feet, and the blocking of normally develops 

 impulses through destruction of afferent pathways in diseases of the spina 

 cord lead at once to make impairment in the coordinating power. Th 

 removal of the skin from the hind legs of the frog, previously deprived of it 

 cerebrum, destroys its coordinating power, which it would otherwise posses 

 in a high degree. 



The blocking, in consequence of destructive lesions of the spinal cord 

 of the impulses, which come from the muscles, tendons, etc., and which infoni 

 us of the activity and the degree of activity of our muscles, the location o 

 limbs, ^ the amount of effort necessary to produce a given movement, etc, 

 also gives rise to much incoordination. A blocking of both tactile am 

 muscle impulses frequently exists in degeneration or sclerosis of the posterio 

 columns of the spinal cord. The coordinating power is so much impairs 

 in this disease that the patient is unable to maintain, without strained effort 

 the erect position and especially if the directive power of the eyes be removet 

 by closure of the lids. Walking becomes extremely difficult; the gait i 

 irregular and jerky, and equilibrium is maintained only by keeping th< 

 eyes fixed on the ground in front and by artificially increasing the basis o 

 support by the use of canes. 



An interference with the development of the customary visual impres 

 sions which in a measure maintain the sense of relation of the individua 

 to surrounding objects also gives rise to equilibratory disturbances, j? 

 rapid change in the relation of the individual to surrounding objects or th 

 reverse; a change in the direction of one optic axis from the use of a prisn 

 or from paralysis of an eye muscle; the destruction of an eye these an< 

 similar conditions frequently give rise to such marked disturbances of th< 

 equilibratory power that displacement is difficult to prevent. 



An interference with the development of the so-called labyrinthine im 

 pressions by destruction of the semicircular canals gives rise to the mos 

 remarkable disturbances in this respect. Section of one horizontal canal 

 in the pigeon is followed by oscillations of the head in a horizontal plant 

 around a vertical axis. Bilateral section so increases these oscillations tha 

 the pigeon is unable to maintain equilibrium and forced to fall and turn con 

 tinuously around the vertical axis. Bilateral section of the posterior vertica 

 canals gives rise to oscillations around a horizontal axis which frequently be 

 come so exaggerated as to eventuate in the turning of backward somersaults 

 head over heels. Similar phenomena follow division of the superior vertica 

 canals. 



Bilateral destruction of both sets of canals is attended by extraordinary 

 disturbances in the equilibrium. From the moment of the operation th< 

 animal, the pigeon, loses all control of its motor mechanisms. It can neithe; 

 maintain a fixed attitude nor execute orderly movements of progression; it; 

 activity, continuous and uncontrollable, is characterized by spinning arounc 

 a vertical axis, turning somersaults, dashing itself against surrounding object! 

 until life is endangered. If the animal be protected from injury, these dis 



1 The physiologic anatomy of the semicircular canals is described in the chapter devotee 

 to the ear, to which the reader is referred 



