806 THE CENTRAL NERVOUS SYSTEM 



ready mentioned. For example, if the animal is held up with the hind 

 legs hanging down, these will often exhibit rhythmic flexion and exten- 

 sion movements, with the two limbs acting alternately, as they would 

 in walking or running. This is sometimes called the mark-time reflex. 

 Another complicated movement may be produced by placing the animal 

 in water, when it may make the movements of swimming, but its swim- 

 ming will not be sufficient to keep it on the surface. These swimming 

 movements are more perfect in the spinal frog. 



After complete recovery from spinal shock, the hind limbs are more 

 or less in a condition of extension contracture; the vascular and other 

 visceral reflexes are in perfect condition, and a marked rise in blood 

 pressure occurs when one of the sensory nerves of the hind limb is 

 stimulated an experiment which can be performed in such animals 

 without the administration of any anesthetic, since the animal feels 

 no pain. In female spinal animals impregnation may occur and preg- 

 nancy proceed in normal fashion accompanied by the usual secretion 

 of milk. The significance of this fact will be dwelt upon later. 



SPINAL SHOCK IN MAN 



As we ascend the animal scale we find that recovery from spinal shock 

 takes longer and longer to occur and becomes less and less perfect. In 

 the case of man, recovery is never complete, for a permanent condition, 

 which has been called " isolation dystrophy, " supervenes before the 

 symptoms of shock have been recovered from. The tendon jerks are 

 permanently abolished in complete lesions of the cord in man, and even 

 when the lesion involves only one lateral half of the cord, this reflex 

 is either entirely absent or very feeble on the corresponding side, though 

 normal on the other (Holmes 5 ). Severe lesions above the lower dorsal 

 region practically always leave the legs in a permanently flaccid con- 

 dition, with accompanying atrophy, but sometimes automatic movements 

 of flexion and extension, like those of the mark-time reflex, may set in. 



When the injury of the cord is less severe, the limb musculature is 

 flaccid and toneless for some time, the tendon jerk and the abdominal 

 and cremasteric skin reflexes being entirely absent. After some time, 

 however it may be as early as ten days the muscles begin to reac- 

 quire some tone, and a little later the tendon jerk becomes elicitable. 

 Eegarding the behavior of the flexion reflex after spinal injuries in 

 man, it has been found that the part of it known as the Bakinski reflex 

 is not elicitable after severe lesions, but in those that are less severe 

 a flexion of the great toe may occur on stimulation of the sole. Later 

 this movement may be accompanied by contraction of the hamstrings, 

 and later still, in favorable cases, by flexion at knee and hip. In these 



