248 THE NERVOUS SYSTEM 



white columns of the cord. This function makes it possible for 

 the brain to receive impressions from and send impulses to the 

 periphery. It is to be remembered that most of these impres- 

 sions and impulses are interrupted by spinal nerve cells in their 

 passage between brain and periphery. 



2. Transference. An impression reaching the gray matter of 

 the cord may be transferred (not as in typical reflex action) so 

 as to be felt in an entirely different region from that in which 

 the irritation takes place. Hip joint disease often gives pain 

 in the knee alone. 



3. Reflex Action. The cord may act as a center without the 

 cooperation of the brain. Indeed, by no means do muscular 

 movements cease immediately on removal of the encephalon if 

 the cord and its nerves be left intact. An animal so mutilated 

 possesses no sensation or volition, but for a time the sensory 

 nerves will continue to convey impressions and the motor nerves 

 impulses. Under these conditions impressions (as of heat) are 

 conveyed to the cord by the afferent nerves; the gray matter of 

 the cord receives the impressions and generates motor force 

 which is sent out through the corresponding efferent nerves, and 

 movements result. This is reflex action. The impression is 

 reflected through the cord and manifested in motion without the 

 intervention of sensation or volition. Reference to Figs. 77 and 

 80 shows how reflex action is anatomically possible through the 

 cord connections. Typical reflex action requires anatomically 

 (i) something to produce an impression, (2) a nerve terminal to 

 receive it, (3) a centripetal fiber to convey it, (4) a center to re- 

 ceive and transform it, (5) a centrifugal fiber to convey it to the 

 periphery and (6) a muscle to contract. This remark applies to 

 reflex action connected with the cord, but by common consent 

 reflex action is not limited to the cord and its connections. 



If reflex action be defined as any involuntary manifestation of 

 nerve force consequent upon the reception of an impression (gen- 

 eral or special) by a nerve center, the term must be made to 



