968 CENTRAL NERVOUS SYSTEM 



of recovery. Later the receptive field becomes more and more extensive 

 and the response spreads to additional groups of muscles until the entire 

 leg is thrown into flexion. As it does so the reciprocal inhibition of 

 the muscles antagonistic to the flexors takes place in a normal manner, 

 just as it does in the spinal cat or dog. Finally, however, a stage of 

 recovery is reached in which a phenomenon occurs which is quite unlike 

 anything seen in these animals. It is called the mass-reflex and consists 

 in an extensive spasm of the flexor muscles of the abdomen and lower 

 extremities which is brought about by harmful stimuli applied almost 

 anywhere to the parts of the body affected by the injury. Accompany- 

 ing the response there is a pronounced outburst of sweating in the af- 

 fected regions and if the bladder is as much as half full, a reflex discharge 

 of the urine. The mass-reflex shows that the spinal reflexes have lost 

 their local signature and have consequently become diffuse in their dis- 

 tribution, resembling in this regard the generalized responses of those 

 animals such as the sea anemone (page 830), which possess a nervous 

 system consisting of an asynaptic nerve net. 



In one to five weeks after the flexor responses first appear the tone 

 of the muscles of the limbs begins to recover and may be restored to 

 nearly, but never to equal, the state found in the normal individual. The 

 posture of the limbs is one of slight flexion. At the same time the ten- 

 don jerks become elicitable. These are the only types of extensor re- 

 sponse which have been observed in cases of complete transection of the 

 human spinal cord. During this stage of recovery the contents of the 

 rectum and bladder are voided automatically (Head and Eiddoch 20 ' 42 ). 



The chief difference in the condition of the spinal man and of the 

 spinal cat or dog consists in (1) the character of the flexor response, 

 which in man has lost its local signature, is diffuse, and is elicited from 

 an abnormally extensive receptive field, (2) the flexor position of the 

 limbs at rest; and (3) the absence of extensor responses, i. e., of those 

 responses significant in maintaining the upright position and in progres- 

 sion. It would appear from this that in man the higher centers in the 

 brain have taken over control of the integration of spinal reflexes to the 

 extent of determining the local signature and limiting the spread of 

 these responses and of governing the activities of the extensor muscles 

 in maintaining postural tone and the extensor movements of progres- 

 sion ; whereas in the lower mammals these phenomena may be executed 

 by the spinal cord alone. Further evidence for this view is afforded by 

 cases in which the human spinal cord is incompletely divided. In these 

 individuals, although paralysis and anesthesia is complete, the reflex 

 activities may not differ markedly from those of the lower animals. The 

 mass-reflex is absent, flexor responses retain their local signature, and are 

 accompanied by crossed extension in the opposite limb. The postural 



