322 PRACTICAL PHYSIOLOGY. [LXIX. 



other nervous affections ; so that its presence or absence is a most 

 important clinical symptom. 



(b.) The knee-jerk is readily obtained in a rabbit. 



9. By means of the hand compress the abdominal aorta of a rabbit for a few 

 minutes. There results temporary paralysis of both hind-legs or paraplegia. 

 Soon after the circulation is restored in the cord and lower limbs, the para- 

 plegia disappears. 



LESSON LXIX. 

 SPINAL NERVE-ROOTS. 



1. Functions of the Eoots of the Spinal Nerves. To expose the roots, 

 destroy the brain of a frog, lay it on its belly, and make a median incision in 

 the skin of the back, from the neck to the upper end of the urostyle. Turn 

 back the flaps of skin, and carry the incision down to the spines of the 

 vertebrae. With a scraper or blunt knife remove the muscles along each side 

 of the vertebral column, so as to lay bare the arches of the vertebrae. With 

 a blunt-pointed pair of scissors, or two saw-blades parallel to each other and 

 fitted at a suitable distance into a handle, as devised by Ludwig, cut through 

 the arches of the eighth or last vertebra, taking care not to injure the nerves 

 within the spinal canal. Remove successively from below upwards the seventh, 

 sixth, and fifth vertebral arches, when the tenth, ninth, and eighth spinal 

 nerve-roots will come into view. The posterior roots are larger, come first 

 into view, and cover the anterior. The roots may be separated by a seeker. 

 Select the largest posterior root the ninth and with an aneurism needle 

 carefully place a fine silk thread (say a red one) under it. 



(.) Tighten the ligature near the cord, and observe movement in some part 

 of the body. Divide the nerve between the cord and the ligature, and observe 

 further movements on division. 



(b.) With the thread gently lift up the peripheral or distal end of the nerve- 

 root, place it on well-protected electrodes, and stimulate it with an inter- 

 rupted current. No movement is observed in the muscles of the limb. 



(c. ) Select the posterior root of the eighth nerve, ligature it at some distance 

 from the cord, and divide it on the distal side of the ligature. There is 

 neither contraction of the muscles of the leg nor movement of the body. 

 Place the central stump, i.e., the part still connected with the cord, on the 

 electrodes, and stimulate it, when movements will take place in several parts 

 of the body. 



(d. ) Divide the posterior roots from the seventh to the tenth nerves. Observe 

 that the leg on that side has become insensible. Turn aside the roots of 

 the divided nerves, and expose the anterior roots, which are very thin and 

 slender. Repeat the preceding experiments on the anterior root of the ninth 

 nerve, i.e., place a ligature round it, tighten the ligature, and divide the 

 nerve between the cord and the ligature. Stimulate the distal end with an 

 interrupted current ; this causes contraction of the muscles supplied by this 

 root. 



From the effects of section and stimulation of the nerve-roots, one concludes 

 that the anterior are motor, and the posterior are sensory. (E. Steinach, 

 " Motorische Functionen hint. Spmalnervenwurzeln,"^#%er's^rc/&., Bd. 66, 

 P- 593-) 



