THE SYMPATHETIC AND PARAS YMPATHETIC SYSTEMS 639 



or axon-reflex. Obviously, the stimulus is applied here to normally 

 efferent fibers from which the impulse is then transferred at the central 

 synapses to the efferent fibers of the opposite side. This transfer 

 is made possible by the fact that each preganglionic fiber arriving 

 in this ganglion, divides into two branches, one of which pursues a 

 direct course to the corresponding side of the bladder, while the other 

 makes connections by synapse with the fibers forming the opposite 

 hypogastric nerve. 



On closer analysis, however, it becomes evident that this particular 

 experiment does not prove anything further than that the normal 

 direction of conduction in the hypogastric fibers may be reversed by 

 experimental means. This is not a new fact, because Kiihne has shown 

 that a similar reversion may be effected in the motor nerves of skeletal 

 muscle. It will be remembered that the nerve innervating the gra- 

 cilis muscle divides into two branches, one of which supplies the 

 upper, and the other, the lower end of this muscle (Fig. 74). 'Inas- 

 much as a contraction may be evoked in its upper end by the stimula- 

 tion of the nerve terminals in its lower end, the fibers of this normally 

 efferent branch must be able to conduct the impulses so generated in 

 an afferent direction. It should not be assumed, however, that this 

 reversal of conduction may also take place under perfectly normal 

 conditions. The same statement applies to the manner of conduction 

 within the sympathetic system, because we have not been able to 

 observe these phenomena under other than experimental conditions. 

 There is one reaction, however, which may be of positive value and 

 that is the following: If an irritant, such as mustard oil, is applied to 

 the skin, this area becomes red, swollen, warm and painful in con- 

 sequence of the dilatation of its blood-vessels. These changes may also 

 be brought about after the sensory fibers from this region have been 

 severed, but are much diminished if the sensitiveness in this part is 

 first abolished by a local anesthetic. It appears, therefore, that 

 this vasomotor reaction is not effected in a direct manner, but reflexly. 

 Now, inasmuch as this area may be isolated from its center by the 

 division of its afferent fibers, the resultant dilatation of the blood- 

 vessels must have been brought about by a local reflex accomplished 

 solely with the help of peripheral axons and their collaterals. 1 



1 Bardy, Skand. Archiv fur Physiol., xxii, 1908, 194. 



