404 THE FUNCTIONS OF THE ROOTS OF SPINAL NERVES. 



fixed on a movable stand. To prevent any escape of the cur- 

 rent, slip a fragment of India-rubber sheeting beneath the nerve 

 and electrodes, so as to isolate these from the cord and from 

 the rest of the nerves. Pass a moderately strong interrupted 

 current through the electrodes. If there be no escape of the 

 current, the animal will not move in the slightest. 



06s. III. Repeat the observation with the nerve-root next 

 above (the 8th), with this difference ; place the ligature as near 

 as possible to the walls, of the spinal canal ; divide the nerve 

 between the ligature and the wall, and place the central instead 

 of the peripheral stump on the electrodes. 



Ligature and section, as before, produce movements. A 

 very moderate interrupted current applied to the central stump 

 will produce very considerable movements in various parts of 

 the body, i. e., signs of sensation or reflex action, as the case 

 may be. 



Ligature or section of the posterior roots of spinal nerves 

 produces movements in various parts of the body. Stimulation 

 of the peripheral stump jyroduci'.^ no movement whatever ; stimu- 

 lutinn of the central stump produces considerable movement*. 

 These movement* J>< ///<// *i tuple reflex actions or more compli- 

 cated voluntary movements set going by conscious sensations, are 

 ci-t'tjfucesof centripetal sensor impulses, excited in the posterior 



/>/ roots. 



ohft. IV. Examine now the sensibility of the hind limb on 

 which you have been operating. It will be found that pinching 

 the toes or the skin of the hind surfaces of the limb produces 

 little or no reflex action. The anterior surface of the leg, how- 

 ever, still retains considerable sensibility. 



aba. V. Divide the posterior roots of the 7th and 8th nerves, 

 and also that of the small 10th nerve. The whole limb will 

 now be found to be totally insensible. Movements of the leg, 

 however, may readily bo called forth by pinching the skin of 

 the back, or any other part of the body except the leg itself. 



I>ft'i.inn nfthc posterior roots stops the passage of sensory, but 

 not of motor impulse*. 



Obs. V I. Carefully cut away the posterior roots on which you 

 have been experimenting. The anterior roots, which are thin- 

 ner than the posterior, will now come into view. 



Repeat on one of these anterior roots (9th nerve) Obs. II. 

 Mere touching the nerve will probably produce a movement of 

 the hind limb of that side. This result will at all events follow 

 upon ligature and section. 



Stimulation of the peripheral stump, with even a very feeble 

 stimul'is, will produce tetanus in the limb. 



"/>-. VII. Kcpcat on the anterior root next above 06s. III. 

 '(feet whatever will be produced by stimulating the cen- 

 tral stump. 



