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A TEXTBOOK OF PHYSIOLOGY 



are considerably more lasting and more complex. Below the site cf 

 the lesion there is total loss of sensation in the skin, the skeletal 

 muscles are inert and flabby, the sphincters are toneless, there is 

 increased loss of heat, and the arterial pressure of the animal falls 

 from 40 to 50 mm. Hg. After a few days many of these symptoms 

 pass away. The arterial pressure rises to normal; the sphincters 

 ngain act, so that urine and faeces are passed in a normal manner; 

 the skeletal muscles recover their tone; and sensory stimuli applied 

 to the skin evoke reflex muscular responses. It is upon such an 

 animal that the code of reflex actions has been worked out. A second 

 section of the cord at a lower level does not renew the .shock. The 



FIG. 402. 



A, Scratch reflex interrupted by a brief flexion-reflex. The time of application of 



the stimulus evoking scratch reflex is shown by the lowest signal fine; that for 

 flexion-reflex by line immediately above. Time in fifths. The scratch reflex 

 returns with increased intensity after the interruption. 



B, Similar to A, but the scratch reflex is interrupted later and returns more slowly 



and with marked irregularity in its beat. (From Sherrington's " Integrative 

 Action of the Nervous System," by permission of Yale University Press and 

 Messrs. Constable and Co., Ltd.) 



shock is caused, then, by cutting off the spinal from the higher 

 centres, not by the lesion of the spinal cord itself. The chief reflexes 

 studied have been 



1 . The flexion reflex. A harmful stimulus applied to the hind-foot 

 causes the withdrawal of the foot from the site of injury an action 

 often accompanied by extension of the opposite hind-limb. 



2. The extension reflex. The application of gentle pressure to 

 the pad of the flexed limb induces the movements of extension of 

 that limb, and of flexions of the opposite limb i.e., the movements 

 of walking in the normal animal. 



