CHAPTEE XI. 



. 



ACTION OF THE SPINAL COED AS A NEEVE-CEXTEE. 



Movements in decapitated animals Definition and applications of the term 

 " reflex " Reflex action of the spinal cord History of the discovery of 

 so-called reflex action Question of sensation and volition in frogs after 

 decapitation Character of movements following irritation of the surface 

 in decapitated animals Dispersion of impressions in the cord Conditions 

 essential to the manifestation of reflex phenomena Exaggeration of reflex 

 excitability by decapitation, poisoning with strychnine, etc. Reflex phe- 

 nomena observed in the human subject. 



IT has long been known that decapitation of animals does 

 not immediately arrest muscular action ; and the movements 

 observed after this mutilation present a certain degree of 

 regularity, and, of late years, have been shown to be in ac- 

 cordance with well-defined laws. Under these conditions, 

 the regulation of such movements is effected through the 

 spinal cord and the nerves connected with it. If an animal be 

 decapitated, leaving only the cord and its nerves, there is no 

 sensation, for the parts capable of appreciating sensation are 

 absent ; nor are there any true voluntary movements, as the 

 organ of the will is destroyed. Still, in decapitated animals, 

 the sensory nerves are for a time capable of conducting im- 

 pressions, and the motor nerves can transmit a stimulus to 

 the muscles ; but the only part capable of receiving an im- 

 pression or of generating a motor stimulus is the gray matter 

 of the cord. If, in addition to the Removal of all of the en- 

 cephalic ganglia, the cord itself be destroyed, all movements 

 of voluntary muscles are abolished, except as they may be 



