404 ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD. 



3d, Excitability of the deep parts of the Spinal Cord. The 

 cord having been carefully cut across in the interval 

 between two spinal nerves, and the adjacent cut surfaces 

 scratched, no effect is produced even in the case of the 

 posterior columns, while the excitability of the outer 

 surfaces of these is retained, though less vividly than 

 before. Again, a needle may be passed in any direction 

 through an unsevered cord without producing the slightest 

 effect, provided always the surface of the posterior column 

 is respected. If passed into the latter, pain and convul- 

 sions are noticed as it penetrates the outer layer, but 

 after this it passes through the cord in any direction 

 without effect If, in the course of this experiment, the 

 roots of the nerves were touched, or the nervous matter 

 in their immediate vicinity, effects were induced exactly 

 like those resulting from the direct irritation of those 

 nerves. 



4th, After Death. If the surface of the superior column, 

 or the root of the sensory nerve, be scratched immediately 

 after the last beat of the heart, they do not respond, while, 

 if the application is made to the motor nerve, active con- 

 tractions may for some time take place. 



Dr Brown-Sequard, who met with results identical with 

 those of Chauveau, remarks, that while physiologists had 

 erred in attributing a lively sensibility to the whole pos- 

 terior column, at the same time the stimulus used in his 

 and Chauveau's experiments might be insufficient to elicit 

 the slight sensibility inherent in the internal parts of the 

 cord. It may, however, be safely concluded that the sensi- 

 bility of the spinal cord only exists to any extent on the 

 surface of the posterior columns. 



The reflex action of the spinal cord has been already 

 referred to (page 387). It is the sole act of the cord as a 



