386 THE OUTGO OF ENERGY 



THE EOOTS OF SPINAL NERVES 

 Destroy the brain of a strong, large frog with 

 a seeker. Divide the skin over the vertebral 

 column from the upper end of the urostyle to 

 the level of the fore limbs. Hook back the 

 flaps of skin. Remove the longitudinal muscles 

 on either side of the spines of the vertebrae, thus 

 exposing the bony arches. Saw through the 

 arches of the 8th, 7th, and 6th vertebrae (there 

 are ten vertebrae in the frog, counting the uro- 

 style) in the order named. Clear away the bone 

 and the underlying tissues until the last three or 

 four pairs of roots shall be plainly seen. Grasp 

 the filum terminale and cautiously lift the cord 

 until the spinal nerve roots are clearly displayed. 

 The anterior roots are hidden by the large, 

 superficial posterior roots. The conspicuous pos- 

 terior root which seems to be the last is, in real- 

 ity, the 9th, the next to the last ; the last, or 

 10th, is smaller and lies close to the filum termi- 

 nale. Place a silk ligature about the middle 

 of an anterior and a posterior root on the right 

 side. With single induction currents as stimuli 

 observe that (1) the stimulation of only the cen- 

 tral end of the posterior root calls forth a (re- 

 flex) movement, and (2) the stimulation of only 

 the peripheral segment of the anterior root causes 

 movement. 



