THE SPINAL CORD AS A CONDUCTING PATH 625 



and Thompson 1 have elucidated this matter further by dividing the 

 sense of touch into tactile discrimination and tactile localization. The 

 former term is employed to designate the ability of being able to 

 discriminate between two mechanical stimuli applied simultaneously 

 to the skin. This sensation may be evoked most easily by touching the 

 integument with a compass the points of which have been separated 

 from one another. Tactile localization is the ability accurately to 

 designate the area which has been stimulated. In certain spinal 

 diseases, these two forms of touch sensation have been found to be 

 dissociated. The former was lost, while the latter persisted. In 

 explanation of this phenomenon, it is held that the fibers allotted to 

 touch discrimination, are contained in the posterior tracts of the same 

 side, while those conveying the impulses of touch proper, are included 

 in the anterolateral fasciculi and cross the median line below the 

 medulla. 



In addition to this dissociation of the tactile impressions into 

 touch discrimination and touch localization, the cutaneous sensations 

 may also be divided into two groups, namely, those of touch and those 

 of pain and temperature. The former impulses, as we have just seen, 

 select in part the posterior columns, while the latter appear to enter 

 the cells of the posterior gray matter, whence they attain the tracts 

 of the opposite anterolateral fasciculi. The evidence which may be 

 submitted in support of this view, is the fact that in syringomyelia the 

 sensations of touch and pressure are retained, while those of pain and 

 temperature are lost. In other words, the patient exhibits an anal- 

 gesia and thermo-anesthesia below the seat of the lesion. These 

 symptoms are suggestive, because this disease affects chiefly the gray 

 matter of the cord, causing a vacuolization of the cells and, therefore, 

 a destruction of the connection between the posterior roots and the 

 anterolateral fasciculi of the same and opposite sides. It would seem, 

 therefore, that the loss of the sensations of pain and temperature is 

 dependent in this case upon the fact that they cannot reach their desti- 

 nation on account of this block upon the path usually selected by them 

 in gaining the opposite anterolateral tract. 



The impulses serving the muscle-sense, may also be divided into 

 two groups, namely, .those which pass directly to the cerebellum and 

 always remain subconscious and those which are relayed to the cere- 

 brum and finally involve volition. It has been stated above that the 

 former select the anterior and posterior cerebellar tracts of the lateral 

 funiculus of the same side, while the latter ascend in the posterior 

 columns of the same side. The latter, however, cross finally to the 

 opposite cerebral hemisphere by way of the optic thalamus. Our 

 muscular movements are executed in accordance with the character 

 of the impulses received from our muscles and tendons. This regula- 

 tion is primarily cerebellar, but may be modified by volition, i.e., the 

 activity of our muscles may be controlled by the cerebellum and cerebrum 



1 Brain, 1906; also see: Saunders, Brain, xxxvi, 1913, 166. 



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