1124 



PHYSIOLOGY 



origin in the cells of the posterior root-ganglion, this observation was 

 widely discredited, until it was confirmed by Bayliss for all manner 

 of stimuli. Stimulation of the posterior roots, either before or after 

 they have passed through the ganglia, causes dilatation of the vessels 

 in the area of the supply of the roots, whatever be the nature of the 

 stimulus employed, whether electrical, chemical, or mechanical (Fig. 

 471). This effect is not destroyed by previous section of the posterior 

 roots on the proximal side of the ganglia, showing that the fibres 

 by means of which the dilatation is produced have the same origin 

 and course as the ordinary sensory nerves to the limbs. Since the 



FIG. 471. Effect of excitation of peripheral end of seventh lumbar posterior 



root in the dog. (BAYLISS.) 



Uppermost curve, volume of left hind limb ; next below, arterial 

 blood pressure ; the third line marks the period of stimulation ; bottom 

 line, time-marking in seconds. 



vaso -dilator impulses pass along these nerves in a direction opposite 

 to that taken by the normal sensory impulses, Bayliss has designated 

 them as antidromic impulses. So far this phenomenon of a nerve- 

 fibre functioning (not merely conducting) in both directions is almost 

 without analogy in our knowledge of the other nerve-functions of 

 the body. There is no doubt, however, that similar antidromic 

 impulses are involved in the production of the so-called trophic changes, 

 such as localised erythema or the formation of vesicles (as in herpes 

 zoster), which may occur in the course of distribution of a sensory nerve, 

 and is always found to be associated with changes, inflammatory or 

 otherwise, in the corresponding posterior root ganglia. Moreover 

 evidence has been brought forward that these fibres may take part 

 in ordinary vascular reflexes of the body, that in fact they are normally 

 traversed by impulses in either direction. 



Some observations by Hans Meyer and Bruce tend to indicate 



