466 THE SPINAL CORD. 



termination of the longitudinal fibres of these columns ; but there are 

 several facts which give it a strong degree of probability. The three 

 principal reasons in support of this view are as follows : 



I. The posterior columns, as fully shown by direct experiment, are 

 not the necessary organs of transmission for either sensation or volun- 

 tary motion ; and they are, nevertheless, composed of nerve fibres which 

 run in a longitudinal direction. In all the white columns of the cord, 

 in their deeper parts, where they lie in contact with the gray substance, 

 there are oblique or horizontal fibres, entering or emerging from the 

 gray substance, which may either belong to the anterior and posterior 

 nerve roots, or may be commissural fibres running lengthwise from one 

 part of the cord to the other. 



II. According to Yulpian, 1 if the posterior columns be divided by 

 several transverse sections, at intervals of two or three centimetres dis- 

 tance from each other, the effect of the operation is a singular disturb- 

 ance in the power of locomotion, like what would be produced by a loss 

 of harmony in muscular action. 



III. The most important facts, however, bearing on this question, are 

 those connected with the disease in man, known as locomotor ataxia. 

 In this affection there is a remarkable difficulty in walking, of such a 

 character that the patient's natural gait is altered, and he is no longer 

 sure of his movements. He loses more or less the power of equilibrium, 

 and cannot guide his foot to a particular point without looking at it 

 and at the same time making a direct effort of the will. Consequently 

 locomotion, as it is usually performed, becomes impossible ; and yet the 

 patient has not lost the power of voluntary movement in any degree, 

 since he can often exert as much muscular force as ever in grasping an 

 object or in simply pushing or pulling with his legs or arms. But he 

 has lost the power of guiding his movements by an involuntary combi- 

 nation, so as to perform with ease the act of ordinary locomotion. It 

 is for this reason that the affection is called " ataxia," and not paralysis. 



In this disease the only parts of the nervous system which are always 

 found to be affected are the posterior columns of the spinal cord. They 

 are the seat of a structural degeneration termed " sclerosis," in which 

 the elements of the connective tissue are increased in quantity and den- 

 sity, while the nerve fibres are altered and atrophied, or finally disappear 

 altogether. According to Brown -Sdquard, an alteration limited to a 

 small extent of the posterior columns does not usually affect the volun- 

 tary movements ; but if it extend for a few inches in length, in either 

 the cervical or the dorso-lumbar region, it always causes a disturbance 

 of these movements ; and when it occupies the whole length and thick- 

 ness of these columns, the patient can neither stand nor walk, although 

 while lying down and with the aid of vision he can move his limbs 

 freely in any direction. 



1 Leqons sur la Physiologie du Systfeme Nerveux. Paris, 1866, p. 381. 



