CONDUCTING PATHWAYS IN THE SPINAL CORD 



589 



shock applied where the current of injury was weak. This relationship would 

 not hold if the stimulus were to traverse root fibers directly, and since it could 

 not have come by way of the posterior columns or afferent fibers, the conclu- 

 sion is that the stimulus was initiated in the efferent 

 fibers of the cord itself. 



It might be objected that the effect in this ex- 

 periment was due to excitation of the gray matter. 

 But this objection is met by the circumstance that the 

 gray matter left in the anterior half showed approxi- 

 mately the same degree of excitability at whatever level 

 it was stimulated. 



Gotch and Horsley have found by stimulation of 

 the long efferent paths of the spinal cord that the rate 

 of propagation in the cord is 39.5 m. per second. 



B. METHODS OF DETERMINING THE CONDUCT- 

 ING PATHWAYS IN THE SPINAL CORD 



We have several fundamentally different meth- 

 ods of determining the location of the conduction 

 pathways, which supplement each other very nicely. 

 They may be summarized under the following three 

 heads : 



A. Anatomical Methods. To these belong: 1. 

 The method first employed by Stilling of making 

 serial microscopical sections of the cord and tracing 

 out the course of the separate fibers from one section 

 to another. 2. A method first used extensively by 

 Flechsig, which is based upon the fact that tracts 

 having the same function acquire their medullary 

 substance at about the same time in the embryonic 

 or post-embryonic development. Fig. 261 represents 

 schematically the organization of the cord as made 

 out by this method. 



B. Pathological-anatomical and Clinical Methods. 

 Here belong: 3. Observations on patients suffering 

 from diseases of the central nervous system, and com- 

 parison of these observations with the post-mortem 

 findings. The observations fall into two divisions, 

 namely : 



(a) Where the patient lives long enough for 

 Wallerian degeneration to develop in the tracts of the 

 cord. Post-mortem examination then gives us the 

 same sort of information as the method based upon 

 development of the medullary substance. In Fig. 



262 is represented the degeneration in the long motor tracts following upon 

 lesion of the cerebral cortex. 



(&) Even if the patient does not live long enough for degeneration to be 

 far advanced, comparison of the symptoms with the lesions found in the cord 



f>3 



FIG. 261 . Cross - sections 

 at different levels of the 

 spinal cord, after Flech- 

 sig. /, at the point of 

 exit of the sixth cervical 

 nerve ; //, at the point of 

 exit of the third thoracic 

 nerve; ///, level of the 

 sixth thoracic; IV, of the 

 twelfth thoracic; V, of 

 the fourth lumbar, ps, 

 crossed pyramidal tract; 

 pv, direct pyramidal 

 tract; ks, lateral cerebel- 

 lar tract; g, posterior 

 column of Goll. 



