THE SPINAL CORD AS A REFLEX CENTRE 373 



SPINAL SHOCK 



If the spinal cord of the frog be divided just below the medulla, 

 for some minutes after the section all four limbs are perfectly flaccid, 

 and it is impossible to evoke any reaction by the application of the 

 strongest stimuli. If the animal be left to itself for half an hour 

 there is a gradual return of reflex tone ; the animal draws up its legs and 

 assumes a position not far removed from that of the normal frog, 

 the head being lower than under normal conditions. We may say 

 that the phenomena of shock in the frog last only a short time. With 

 increasing complexity of the nervous system the phenomena of 

 shock become more lasting, so that among laboratory animals it is 

 in the monkey that spinal shock is most apparent. It is interesting 

 to note, as pointed out by Sherrington, that shock appears to take 

 effect only in the aboral direction. Thus, even in the monkey, section 

 through the lower cervical region, though causing profound paralysis 

 of the lower limbs and part of the trunk, apparently has no influence 

 at all on the reactions of the nervous system above the section. " The 

 animal immediately after the section will contentedly direct its gaze 

 to sights seen through the window, or, if the section have been below 

 the brachial region, may amuse itself by catching flies on the pane. 

 This is the more remarkable since the profound depression of the 

 nerve-centres below the point of section extends also to the blood- 

 vessels and viscera, so that there is a great fall of blood pressure 

 and diminished production with increased loss of heat. The sphincters 

 are flaccid or patulous, the skeletal muscles are toneless, and no 

 reaction is evoked by the strongest stimulus to the- skin or to a sensory 



nerve. " 



Much discussion has arisen as to the duration of shock. Goltz 

 and others imagined that the phenomena of shock may persist for 

 months or even years. According to Sherrington, in the higher 

 animals the phenomena of shock are complicated by the onset of 

 an " isolation dystrophy " which may occur before the condition of 

 shock has entirely disappeared. In order therefore to examine the 

 capabilities of the isolated spinal cord at their best, a time must 

 be chosen when the sum of shock and isolation dystrophy together 

 is at its minimum. 



The occurrence of shock after complete transection of the cord 

 in the cervical region cannot be ascribed to the fall of blood pressure 

 which ensues as a result of the severance of the efferent vaso-motor 

 tracts from the vaso-motor centre in the medulla. The centres above 

 as well as those below the transection are equally exposed to the 

 effects of the lowered blood pressure, but it is only those below the 

 section which show signs of shock. Nor can it be regarded as operative 



