REFLEX ACTION OF THE SPINAL CORD. 815 



" knee-jerks," after the temporary period of " shock " is over, are more 

 brisk than normal. Stimulation of the foot evokes drawing up of the leg 

 and flexion at the hip and knee just as in the frog. The drawing up of 

 the limb stimulated is accompanied usually by the pushing down of the 

 opposite limb (active extension at hip, knee, and ankle), just as is often 

 the case in the frog. To lift the animal by the fore-limbs frequently 

 evokes rapid alternating flexion and extension of the hind-limbs like that 

 observed in birds. The weight of the limbs probably produces tensions 

 that are adequate and sufficient stimuli for apparatus of "muscular 

 sense " within the limbs. The movements thus started can be brought 

 to a standstill by strong " pathic " stimuli to skin, etc. When in the cat 

 or monkey a " limb-region " of the cord has been isolated, reflex move- 

 ments of the apex of the limb are easily obtained : the reflex movement of 

 hallux and pollex of the monkey is commonly adduction-flexion, often 

 combined with dorsal flexion of the basal-phalangeal joints. Extension 

 of the wrist is not uncommon. In the cat and rabbit spreading of the 

 digits in response to a touch on the foot is common ; this is sometimes 

 bilateral. Flexion at knee and adduction at hip are elicitable from 

 almost the whole skin-field of the limb, but are feebler in the monkey 

 than in the cat and dog. Irritation of the perineum elicits protrusion of 

 the anus. Defsecation in the paraplegic monkey, as in the dog, soon 

 becomes regular and efficient ; it can sometimes be excited by irritation 

 of the anus, but usually more effectually by pressure upon the bladder, 

 and so probably upon the rectum, through the ventral abdominal wall 

 above the pelvis. The act is generally accompanied by elevation of the 

 tail and flexion at hips and knees, and is followed by lateral move- 

 ment of the tail. Micturition comes, after an interval immediately 

 succeeding the spinal transection, to be fairly easily initiated and 

 performed. On the crossed side to that excited, there occurs in the 

 monkey quite frequently, as in the dog and cat, extension at hip and 

 knee synchronous with the homonymous flexion ; adduction of the 

 contra-lateral thigh occurs with perhaps peculiar frequency in the 

 monkey. The cremasteric reflex is well seen in the monkey. In all 

 types it is very usual for a touch on the side of the tail to evoke 

 a lateral movement of the tail, abducting it from the side stimulated, 

 and for the tail to be depressed and drawn to the homonymous side on 

 stimulation of the surface of the hind-limb. 



If the isolated length of the spinal cord be thoracic, skin stimuli 

 can in the dog evoke contraction of the lateral muscles, causing 

 incurvation of the trunk with concavity toward the side of the excita- 

 tion. 1 Skin stimuli to the front of the thorax and back evoke " shak- 

 ing " of the trunk, much like the movement made by a dog on 

 coming out of water, twitching of the panniculus carnosus, and, by 

 application of cold, a shivering confined to the musculature innervated 

 by the isolated length of the cord. After high thoracic transection, 

 rubbing the skin, especially on the side of the chest or scapula, evokes 

 a "scratch" reflex, namely, rapid alternating flexions and extensions 

 at ankle with protraction of the limb ; this is a homonymous unilateral 

 reflex, but reflexes obtained from the skin on the ventral surface of 

 abdomen and thorax usually affect the limbs bilaterally. 



Stimulation of a single afferent thoracic root evokes contraction 

 in muscles, limited, roughly speaking, to the area of the corresponding 



1 Sherrington, Phil. Trans., London, 1892. 



