CONDUCTING PATHS IN THE SPINAL CORD. 739 



The exact division-experiments of C. Ludwig and Woroschiloff, Ott and 

 Meade Smith demonstrated in the rabbit that in the lower dorsal portion of the 

 cord the course of the fibers is exclusively in the lateral column. Partial division 

 of the lateral column abolishes voluntary movement in individual related muscles 

 below the level of the section. From what has already been stated it will be 

 clear that the lateral columns increase progressively in size and in the number 

 of fibers they contain from below upward. In the anterior horn every motor 

 fiber enters into relation with one ganglion-cell, as has been demonstrated in the 

 frog. 



The fibers that intermediate the tactile, widespread, coordinated re flexes 

 enter through the posterior roots and then pass to the columnar cells. 

 At the various levels of the cord, the groups of ganglion-cells that con- 

 trol the coordinated reflexes are further connected by fibers that for the 

 extremities pass within the anterior mixed tracts of the lateral column 

 (the ground-bundle of the anterior column ?) and for the trunk in the 

 posterior column. From the motor ganglion-cells the fibers for the 

 stimulated muscles pass through the anterior roots. 



Ataxic tabes dorsalis, in which, principally on a syphilitic basis, degeneration 

 of the posterior columns is encountered, is noteworthy on account of its charac- 

 teristic motor disturbances. Voluntary movements can, it is true, be executed 

 with full strength, but they lack the fine harmonious gradation with reference to 

 intensity and extent. This function is in part subserved by the normal existence 

 of tactile sensations and of the muscular and articular sense, the paths for which 

 are situated in the posterior columns. After degeneration of the latter, not only 

 anesthesia, but also derangement in the execution of the tactile reflexes, occurs, 

 as the centripetal segment of the arc is interrupted. Also the tone of the muscles, 

 which depends essentially upon reflex stimulation, is considerably lowered, and in 

 consequence the muscles exhibit an excessive degree of passive extensibility. An 

 associated lesion of the simply sensory nerves, however, may in an analogous 

 manner, as a result of anesthesia and loss of the pathic reflexes, give rise also to 

 disturbances in coordination of movement. As the fibers of the posterior roots 

 pass through the white matter of the posterior columns, it will thus be clear that 

 disorders in the sensory sphere occur as a result of degeneration of these parts. 



The view also is maintained by some that tabes represents a disease of the 

 posterior roots extending to the spinal cord, for the roots also are found involved 

 in the degenerative process, and their involvement may be responsible for the 

 derangement in the sensory sphere. The latter consists in part in an abnormal 

 increase of tactile or pain impressions, associated with lancinating pains, while 

 in part it may be increased to the point of anesthesia or analgesia. At the same 

 time tactile sensibility is altered, in consequence of irritation of the posterior 

 columns, as indicated by sensations of numbness, softness, formication, or con- 

 striction. Often sensory conduction is delayed. The sensibility of the muscles, 

 joints and internal parts is altered. If, finally, the posterior columns really 

 contain fibers for the conduction of widespread coordinated reflexes, the ataxia 

 can be explained in part by an interruption of these paths. The exceedingly rare 

 cases of tabes without sensory derangement are to be interpreted only by assuming 

 that either the conducting paths of the coordinated reflexes or the ganglion-cells 

 are injured. 



Inhibition of the tactile reflex takes place through the tracts of the 

 anterior columns. At the proper level the conducting fibers pass from 

 the anterior column into the gray matter, in order to enter into contact 

 with the fibers of the reflex apparatus. 



The transmission of pain impressions takes place through the pos- 

 terior roots and thence through the entire gray matter. Loss of pain or 

 of thermal sensibility occurs in man as a result of disease of the spinal 

 cord in or near the posterior horn. In part decussation of the fibers 

 that pass from one side to the other takes place in the cord. Their 

 further course to the brain is described on p. 745. 



