REFLEXES l\ THE SPINAL ANIMAL AND SPINAL BH(X 807 



eases also the Babinski reflex changes From a flexion to an extension 

 of the great toe. It is important to note in connection with the above 

 association of movements, thai the sensory area of the sole is connected 

 with the same segment of the Bpinal cord that famishes the mi I 

 fibers to the flexors of the toes and the hamstrings (first sacraL) The 

 overy after shock therefore sets in earlier for onisegmental n-fiVx 

 areas than for those involving several segments. 



The Cause of Spinal Shock 



The relationship of the profundity of spinal shock to the phylogenetic 



position of the animal indicates that the shock must be due to the 

 isolation of the lower spinal segments from the higher centers (Pike'V 

 Tt has been suggested that the spinal section in the hitrher but not in 

 the lower animals breaks a nervous pathway in which normally the 

 reflex impulses travel. According to this view, the afferent impulse, 

 when it enters the spinal cord in the lower animals, chooses the shortest 

 possible route to the effector neuron of the same or closely adjacent seg- 

 ments by the collateral branehes springing from the sensory neuron. 

 In the higher animals, however, it would appear that, although this local 

 spinal pathway is present and may be taken, yet it is usually passed 

 by and the impulse travels up to the higher centers, from which it is 

 then transmitted by the pyramidal tracts to the motor neurons con- 

 cerned. This would appear to he the pathway for nervous reflex im- 

 pulses in higher animals the beaten track. When the spinal cord is 

 severed, therefore, the condition of shock supervenes because impulses 

 have not yet learned that they may find a shorter road to the motor 

 neuron by the collateral than by the pathway which they usually travel. 

 They learn this only after some time, which explains the slow 

 COVery of the reflexes from shock. 



It is obviously a difficult matter to supply direct proof in support of 

 the above hypothesis of the cause of spinal shock, but besides the in- 

 direct evidence furnished by observations on the degree to which this 

 condition supervenes in different groups of anmials, the hypothi 

 also conforms well with all the other facts which we know regarding 

 the condition. For example, it is well known that the portion of the 

 body above the transection of the spinal cord in no way suffers from 

 the shock. Sherrington has described s monkey the cord of which was 

 cut below the cervical region, and which immediately after the opera- 

 tion amused itself by catching flies with the ant rtremities, wher 

 the posterior extremities were in a condition of the profoundeai shook. 

 Such experiments further indicate that the shock can not be dependent 



