840 



THE SPINAL CORD. 



" Lemons sur la physiologie du systeine nerveux," that each part of the cord 

 exerts a restraint upon the other parts. 



In the spinal crayfish the movement of the leg is at once stopped by touch- 

 ing the tail. 1 Goltz's reflex inhibition of the heart beat by striking the 

 abdomen of the frog does not occur if at the same time the foot is pinched. 

 The "spinal" snake, suspended by its head, makes rhythmical pendulous 

 movements; these cease when the body is lightly touched. In the spinal 

 dog a severe squeeze of the tail or hind-foot will interrupt micturition 

 already in progress. Such a stimulus must be regarded as " pathic " ; 

 it often fails to inhibit, but it often succeeds. It is not observable in 

 the bird, nor have I obtained it in the monkey. A more regularly 

 obtainable example, which, moreover, does not require the use of strong stimuli, 

 is the following. In the spinal cat (or frog) excitation of the skin of the 

 foot, when the limbs hang down, causes drawing up of the homonymous and 



Fig. 358. — Diagram of the predominant uncrossed flexor reflex of the hind-limb 

 inhibiting the crossed extensor reflex otherwise obtainable by stimulation of 

 the opposite limb. 1, The initial pose of the spinal animal; 2, the pose 

 assumed after stimulation of the left hind-foot, the flexors of the left hip, 

 knee, and ankle, and the extensors of the right hip, knee, and ankle are in 

 active contraction ; 3, the pose assumed after simultaneous stimulation of 

 both hind-feet. The extensor action of the hip, knee, and ankle that would 

 appear from either side as a crossed reflex is bilaterally inhibited, and the 

 antagonistic flexor reflexes bilaterally prevail. 



extension of the contralateral limb. If both feet be stimulated simultaneously, 

 the contralateral extension does not occur, the extensors are inhibited and 

 the flexors of both sides are thrown into contraction. This experiment 

 seems to be in some sort a converse to that in which one leg of a spinal frog is 

 stimulated by a ligature or acid, while the other is lightly pinched. The latent 

 time for the reaction of the pinched leg is then lengthened, or, with a particular 

 strength of stimulus, the reaction does not occur. 



After spinal transection, inhibition of skin reflexes by peripheral excitation 

 of other surfaces is after a time unobtainable, so great becomes the reflex 

 excitability. On stimulation of the pinna or fore-limb after semisection 

 in the thoracic region, the movement of the hind-limb, which previous to 

 semisection is less elicitable contralateral^ than homonymously, I found be- 

 came easier contralaterally. 



It is probable that inhibition of one spinal " centre " by another plays a 

 great part in the elementary co-ordination of actions executed under spinal 

 1 J. Ward, Joum. Physiol., Cambridge and London, 1879, vol. ii. 



