NERVOUS CONTROL OF THE BLOOD-VESSELS 999 



whether electrical, chemical, or mechanical (Fig. 466). 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 imbs. Since the 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 





FIG. 466. Effect of excitation of peripheral end of the 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. 



involved in the production of the so-called trophic changes, such as localised 

 erythema or the formation of vesicles (as in herpes zister], 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 that in 

 the antidromic vaso- dilatation, as well as in the reddening and inflammatory 

 changes ensuing on local excitation, we are dealing with axon reflexes, perhaps 

 the only remains of the local reflexes of a primitive peripheral subcutaneous 

 nervous system. If croton oil or mustard oil be applied to the skin or to the 

 conjunctiva, redness, swelling, and all the signs of a local inflammation are 

 produced. The course of events is not altered by destruction of the central 

 nervous system or by section of the sensory nerve-roots (posterior spinal 

 root or trigeminus) on the central side of the ganglion. If, however, they 

 be divided peripherally of the ganglion, and time be allowed for complete 



