322 



PHYSIOLOGY 



CHAP. 



currents, and alternating currents of high frequency. The reflex 

 consists in a series of short rapid contractions of the flexors of the 

 hip, the frequency of which is independent of that of the excitation. 

 The reflex path runs, as shown by the method of successive sections, 

 in the external part of the lateral column. 



The chief characteristic of this reflex is that one and the same 

 reaction can be elicited from a comparatively large sensory area 

 (Sherrington's receptive field), so that a whole series of afferent 

 (sensory) mechanisms are in connection with the same efferent 

 (motor) mechanism. 



" At the commencement of every reflex arc," Sherrington writes, 

 " is a receptive neurone extending from the receptive surface to 

 the central nervous organ. This neurone forms the sole avenue 

 which impulses generated at its receptive point can use whitherso- 



FIG. 185. Receptive field for scratch reflex in dog with complete cervical 

 transaction. (Sherrington.) 



ever be their destination. This neurone is therefore a path 

 exclusive to the impulses generated at its own receptive point, and 

 other receptive points than its own cannot employ it. 



" But at the termination of every reflex arc we find a final 

 neurone, the ultimate conductive link to an effector organ, muscle, 

 or gland. This last link in the chain, e.g. the motor neurone, 

 differs obviously in one important respect from the first link of 

 the chain. It does not subserve exclusively impulses generated at 

 one single receptive source, but receives impulses from many 

 receptive sources situate in many and various regions of the body. 

 It is the sole path which all impulses, no matter whence they 

 come, must travel if they are to act on the muscle-fibres to which 

 it leads. . . . 



" Eeflex arcs show, therefore, the general features that the 

 initial neurone of each is a private path exclusively belonging to a 

 single receptive point (or a small group of points) ; and that finally 

 the arcs embouch into a path leading to an effector organ ; and 



