5 2o TEXT-BOOK OF PHYSIOLOGY. 



connected with (4) the general musculature of the body. Both station 

 and progression are directly dependent on the development and trans- 

 mission of afferent impulses from the previously mentioned periph- 

 eral sense-organs to the cerebellum. Tactile, muscle, visual, and 

 labyrinthine impressions and sensations not only cooperate in the 

 development and organization of the motor adjustments necessary 

 to the maintenance of the equilibrium and locomotive coordination, 

 but even after their organization they are necessary to the excitation 

 of cerebellar activity. The manner in which they lead to the develop- 

 ment of this capability on the part of the cerebellum is conjectural. 

 Their ever-present influence is shown by the effects which follow their 

 removal, as the following facts indicate. 



The prevention of the development of tactile impulses by freezing 

 or anesthetizing the soles of the feet, and the blocking of normally de- 

 veloped impulses through destruction of afferent pathways in diseases 

 of the spinal cord lead at once to marked impairment in the coordinat- 

 ing power. The removal of the skin from the hind legs of the frog, 

 previously deprived of its cerebrum, destroys its coordinating power, 

 which it would otherwise possess 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 inform us of the activity and the degree of activity 

 of our muscles, the location of the limbs, the amount of effort necessary 

 to produce a given movement, etc., also gives rise to much incoor- 

 dination. A blocking of both tactile and muscle impulses frequently 

 exists in degeneration or sclerosis of the posterior columns of the 

 spinal cord. The coordinating power is so much impaired 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 

 removed by closure of the lids. Walking becomes extremely difficult ; 

 the gait is irregular and jerky, and equilibrium is maintained only 

 by keeping the eyes fixed on the ground in front and by artificially 

 increasing the basis of support by the use of canes. 



An interference with the development of the customary visual 

 impressions which in a measure maintain the sense of relation of the 

 inolividual to surrounding objects also gives rise to equilibratory dis- 

 turbances. A rapid change in the relation of the individual to sur- 

 rounding objects or the reverse; a change in the direction of one 

 optic axis from the use of a prism or from paralysis of an eye muscle ; 

 the destruction of an eye; these and similar conditions frequently 

 give rise to such marked disturbances of the equilibratory power that 

 displacement is difficult to prevent. 



^ An interference with the development of the so-called labyrin- 

 thine impressions by destruction of the semicircular canals gives rise 

 to the most remarkable disturbances in this respect. Section of one 



