CHAP. XI.] MECHANISM OF THE ACTION OF THE CORD- 321 



Experiment, while it fails to elucidate the function of the pos- 

 terior column,, exhibits nothing in opposition to the views we have 

 expressed. It is not to be expected that commissural and co- 

 ordinating fibres should react with stimuli similarly to fibres of 

 voluntary motion. 



We think that the phenomena of disease may be referred to in 

 support of our view. In many cases where the principal symptom 

 has been a gradually increasing difficulty of walking, the posterior 

 columns have been the seat of disease. We may notice two kinds 

 of paralysis of motion, distinguished respectively by impairment or 

 loss of voluntary motion, and of the power of co-ordinating move- 

 ments. In the latter form, while the voluntary powers are con- 

 siderable, the patient walks with great difficulty, and a gait so 

 tottering that his centre of gravity is easily displaced. These cases 

 are generally of the most chronic kind, and many of them go on 

 from day to day without any increase of the disease or improve- 

 ment in their condition. In two examples of this variety we ven- 

 tured to predict disease of the posterior columns of the cord : and 

 this was found to exist on a post-mortem inspection. All cases on 

 record, which we have had the opportunity of examining, in which 

 the posterior columns were the seat of disease, began by evincing 

 more or less disturbance of the locomotive powers ; and it seems to 

 us that the degree to which sensibility may become affected will 

 greatly depend upon the extent to which the posterior roots of the 

 nerves are involved in the disease. 



The hypothesis, then, which we are most disposed to adopt, is the 

 following: That the ant ero -lateral columns of the spinal cord with 

 the gray matter are, in connexion with the brain, the recipients of 

 sensitive impressions and volitional impulses, and that they are 

 the centres of the independent or physical nervous actions of 

 the cord; and that the posterior columns propagate the influence 

 of that part of the encephalon which combines with the nerves 

 of volition to regulate the locomotive powers, and serve as 

 commissures in harmonizing the actions of the several segments of 

 the cord. 



What is the mechanism of these actions of the spinal cord 

 mental, physical, locomotive ? This is a problem of the highest 

 interest, bearing upon the mechanism by which nervous power 

 developed in any nervous centre, as well as in the cord, is capable 

 of affecting peripheral parts ; and it is on that account well deserv- 

 ing the most patient investigation. 



Wo assume, as necessary postulates, preliminary to the discussion 



VOL. i. Y 



