330 PHYSIOLOGY 



an incomplete and maimed system, the incompleteness increasing as we 

 ascend the scale of animals in our experimentation, owing to the increasing 

 subordination of the lower to the higher centres, and of the immediate 

 reflexes to the educated reactions of the anterior part of the brain. 



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 impos- 

 sible 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 in- 

 teresting 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 imme- 

 diately 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 pres- 

 sure, but it is only those below the section which show signs of shock. Nor 

 can it be regarded as operative shock due to the severity of the lesion ; such 

 an operative shock would be effective in either direction, and we do not 



