FUNCTIONS OF THE SPINAL CORD AS A CONDUCTOR. 679 



posterior limbs are still sensitive, though evidently less than in the normal condition." 

 (Brown-Sequard.) 



It is impossible to divide the gray matter of the cord alone, without injuring, more or 

 less, the white substance; but, when the gray matter is divided with very slight injury 

 of the white substance, sensibility in the parts below the point of section is totally 

 destroyed. As regards the part of the gray substance specially concerned in the trans- 

 mission of sensory impressions, the results of experimental investigation have not been so 

 definite ; but Brown-S6quard is of the opinion that the transmission takes place chiefly 

 in the gray matter surrounding the central canal, while it may also occur to some extent 

 in other portions. 



The answer to the third question is deduced from the answers to the first two. The 

 gray matter and the white substance of the cord do not participate in the transmission 

 of sensory impressions, this being eifected by the gray substance, especially its central 

 portion, to the exclusion of the white. 



The precise office of the posterior white columns of the cord is still a matter of con- 

 jecture. If these parts be insensible, except on the surface and near the posterior roots 

 of the nerves, and if they take no part in the transmission of sensory impressions to the 

 brain (which seems to have been conclusively proven), what is their function ? 



The anatomical relations of the posterior white columns, the results of experiments 

 upon living animals, and certain well-marked pathological phenomena, point very strongly 

 to a connection between these columns and the coordination of muscular movements. 



Probable Function of the Cord in Connection with Muscular Coordination. Anato- 

 mists have not been able to trace satisfactorily the direction of all of the fibres contained 

 in the posterior columns ; but it is probable that at least some of these fibres serve as 

 longitudinal commissures, and connect together the nerve-cells, extending for a greater 

 or less distance both upward and downward in the cord. This anatomical arrangement 

 is rendered probable chiefly by the results of experiments. 



If the posterior columns be completely divided, by two or three sections made at inter- 

 vals of from three-fourths of an inch to an inch and a quarter, the most prominent effect 

 is a remarkable trouble in locomotion, consisting in a want of proper coordination of 

 movements. 



In the remarkable disease known under the name of locomotor ataxia, there is a very 

 peculiar condition of the muscular system, in which, while the power of the muscles is 

 but slightly diminished, the movements of progression show great deficiency in coordi- 

 nating power, frequently attended with more or less disturbance in the sensibility of the 

 parts affected. These symptoms are associated with structural disease of the cord, gen- 

 erally limited to the posterior columns and the posterior roots of the spinal nerves. 



Many years ago, before locomotor ataxia had been generally recognized by patholo- 

 gists, Todd made the following remarkable statement with regard to the posterior col- 

 umns : " I have long been impressed with the opinion, that the office of the posterior 

 columns of the spinal cord is very different from any yet assigned to them. They may 

 be in part commissural between the several segments of the cord, serving to unite them 

 and harmonize them in their various actions, and in part subservient to the function of 

 the cerebellum in regulating and coordinating the movements necessary for perfect loco- 

 motion." Todd farther states that this view is supported by the phenomena observed in 

 cases of disease " distinguished by a diminution or total loss of the power of coordinating 

 movements. ... In two examples of this variety of paralysis, I ventured to predict 

 disease of the posterior columns, the diagnosis being founded upon the views of their 

 functions which I now advocate ; and this was found to exist on post-mortem inspection ; 

 and in looking through the accounts of recorded cases in which the posterior columns 

 were the seat of lesion, all seemed to have commenced by evincing more or less disturb- 

 ance of the locomotive powers, sensation being affected only when the morbid change 



