SUMMARY, MAMMALIAN NERVOUS SYSTEM; SPINAL SHOCK 967 



animal, however, the reflex always occurs provided an adequate stimulus 

 is applied. 



The extensor thrust is elicited by applying pressure to the pad of the 

 paw or the sole of the foot. It consists of a quick extension movement 

 of the corresponding limb usually with a flexion of the opposite limb. 



After complete recovery from shock, the paralyzed parts of the body 

 are capable of performing even more complex movements than those al- 

 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. 



Spinal Shock and the Recovery of Reflexes in Man 



The potentialities of the spinal cord of man have not been fully 

 realized until recent years when investigations by Head and Riddoch 42 on 

 men who had been shot through the spine have shown just how complete 

 a recovery can be made from such an injury if the patient is given proper 

 care. In cases of complete transection of the cord there usually re- 

 sults in man, as in the other mammals, a complete loss of reflex activity 

 and of tone in those parts of the body innervated from segments of the 

 cord which lie below the lesion. Occasionally the cremasteric and 

 bulbocavernous reflexes may still be elicited. Below the lesion there is 

 complete anesthesia, the skin is dry and readily becomes gangrenous, 

 and the urine and feces are retained. After a period varying from one to 

 three weeks the first reflexes reappear. These are the flexion reflexes in 

 response to harmful stimuli. At first they can be elicited only from the 

 part of the receptive field which normally is most sensitive, i. e., the sole 

 of the foot, and involve those muscle groups which are normally brought 

 into play by the weakest stimuli. Movements of the toes are conse- 

 quently the only part of the reflex figure to display itself in the earliest stage 



