SPINAL COED 417 



experimenting with lower animals, and by the study of 

 human beings whose nerve tracts have become diseased in 

 part, it has been found possible to locate the tracts where 

 sensory impulses are translated into consciousness, and 

 also the points of origin of control impulses for different 

 organs. 



^Localization of functions in the central nervous system. — 

 Such experimental studies as noted above have demon- 

 strated that a sensory impulse produces no conscious 

 sensation imless it reaches a certain area of the brain, and 

 if this area is destroyed and the transmitting fiber with 

 its end organ preserved intact, no sensation results. Sim- 

 ilarty, it has been found that certain organs and parts of 

 the body are under the control of definite areas of the 

 brain and cord, and these areas must be in a healthy con- 

 dition or the action of these organs is seriously interfered 

 with. The determination of these areas of sensation and 

 control is called the localization of functions, and the 

 method by which results have been obtained is largely 

 through experiment with lower animals. 



Spinal cord. — If we cut the spinal cord of the frog just 

 back of the medulla, the frog will continue to live and the 

 heart will continue to beat, but he ceases to breathe or 

 swallow. The animal lies flat on his belly and loses all 

 power of voluntary movement or conscious sensation. He 

 is still able, however, to respond to external stimuli with 

 definite movements. Thus, if we irritate the skin, the 

 animal will make definite and skilful movements to re- 

 move the irritating body; if we pinch the toe, the foot is 

 withdrawn. From these and similar experiments it has 

 been conclusively demonstrated that the cord is the seat 

 of those reflex movements which concern responses to 



EDDY. PHYS. — 27 



