500 



MESSRS. F. GOTCH AND V. HOBSLEY 



A similar increase of the normal latency in the discharge of the cord, we have also 

 observed by the graphic method, and delay of the kind is frequently noticed in the 

 cortex cerebri (FRANCOIS FRANCK) when its activity is depressed by any of the 

 agencies referred to on p. 483. 



SECTION 4. THE INFLUENCE EXERTED BY ITS CENTRAL ATTACHMENTS UPON THE 

 ELECTRICAL CHANGES EVOKED IN A DIRECTLY EXCITED NERVE. 



We found, in the course of our experiments upon the nerve roots, that the amount 

 of the electrical change in the nerve evoked by direct excitation of its fibres in any 

 root, varied with the condition of the nerve centres, and was always less when the root 

 was cut away from its central attachments. 



We, therefore, designed a series of experiments to test the extent of this influence 

 in the case of the anterior and posterior roots respectively. 



This series of experiments consisted in the exposure of the cauda equina, after 

 division of the spinal cord in the dorsal region, connecting the central end of the cut 

 sciatic nerve with the galvanometer, and then raising the posterior roots seriatim, and 

 exciting each with the platinum electrodes under all the precautions stated in 

 Chapter IIL, Section 4. After measurement of the effect observed in the nerve 

 to follow excitation of any posterior root in continuity with the spinal cord, the 

 root was divided about its middle and the peripheral end gently ligatured, raised in the 

 air and excited. The resulting electrical change or effect in the nerve was noted 

 and compared with that obtained from the root when first excited in continuity with 

 the cord. 



In every case a diminution was observed in the effect as a direct consequence 

 of severing the peripheral portion from the central apparatus. We feel justified 

 in attributing this change to the cause assigned since the immediate local effect of the 

 section on the peripheral fibres would be to raise rather than depress their excitability. 

 The result, if marked, although conceivably due to the depressing effects of injury, 

 is possibly associated with a loss of a beneficial (nutritive ?) influence derivable from 

 the spinal centres. The deflections observed were as follows : 



AVERAGES. 



Effect in nerve. 



Posterior root excited. 



6th lumbar 

 7th lumbar 

 1st sacral . 



Root excited in 

 continuity 

 with cord. 



267 

 259 

 212 



Root cut and 



peripheral 



end excited. 



227 



172 



75 



