104 ESSENTIALS OF PHYSIOLOGY. 



spinal cord branch in the ganglion, one branch passing down the left 

 nerve, the other entering into the formation of a cell station connected 

 with the right hypogastric nerve (fig. 32). Stimulation of the central 

 end of the left nerve causes an impulse to pass up to the point of junction 

 of the two branches, and then down the other branch through the cell 

 station to the bladder. This effect is called an axon reflex, and depends 

 upon the fact that nerve fibres may conduct impulses in either direction. 

 The autonomic system also contains afferent fibres, though these 

 are less numerous than the efferent fibres ; in the splanchnic and 

 hypogastric nerves about one-tenth of the fibres are afferent. The 

 stimulation of these fibres by abnormal processes in the abdominal 

 organs may give rise to pain. The pain is usually referred, however, 

 not to the organ itself, but to the surface of the body ; for instance, 

 afferent impulses from the stomach may give rise to pain which is 

 referred to an area of skin at the lower border of the ribs, and this 

 area may actually be tender to touch. The position of the referred 

 pain and of tender cutaneous areas has proved of value in man as a 

 means of localising disease of the internal organs. 



