558 NERVOUS SYSTEM 



inch to an inch and a quarter (20 to 30 millimeters), the most prominent 

 effect is a remarkable trouble in locomotion, consisting in a want of 

 proper coordination of movements. Experiments on the different 

 columns of the cord in living animals, however, are so difficult that 

 physiologists have preferred to take the observations in cases of disease 

 in the human subject as the basis of their ideas in regard to the office 

 of the posterior white columns. 



The characteristic phenomenon of locomotor ataxia is inability to 

 coordinate muscular movements, particularly those of the extremities. 

 There is not of necessity any impairment of actual muscular power ; 

 and although pain and more or less disturbance of sensibility are usual, 

 these conditions are not invariable and they are always coincident with 

 disease of sensory conductors. The characteristic pathological condi- 

 tion is disease of the posterior white columns (columns of Burdach). 

 This usually is followed by or is coexistent with disease of the posterior 

 roots of the spinal nerves and disease of the cells of the posterior gray 

 matter of the cord. As the cells are affected, there follow ascending 

 secondary degenerations in the columns of Goll. It is fair to assume 

 that the disease of the cells of the gray matter of the cord and of the 

 posterior roots of the spinal nerves is connected with the disorders of 

 general sensibility. The disease of the columns of Burdach produces 

 the disorder in movements. 



Reasoning from the characteristic phenomena and the essential 

 pathological conditions of the cord in typical cases of locomotor ataxia, 

 the posterior white columns of the cord, connecting cells of the gray 

 matter in different planes with each other, assist in regulating and 

 coordinating the voluntary movements. The fibres of these columns 

 also connect the cord with the cerebellum, which has an important office 

 in muscular coordination. It is probable that the appreciation of the 

 muscular sense and the sense of pressure, if these can be separated from 

 what is known as general sensibility, are connected with the action of 

 the fibres of the posterior white columns. 



NERVE-CENTRES IN THE SPINAL CORD 



It has long been known that decapitation of animals does not arrest 

 muscular action ; and the movements observed after this mutilation 

 present a certain degree of regularity and have been shown to be in 

 accordance with well-defined laws. Under these conditions, the regula- 

 tion of such movements is effected through the spinal cord and the spinal 

 nerves. If an animal is decapitated, leaving only the cord and its nerves, 

 there is no sensation, for the parts capable of appreciating sensation are 



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