x VASCULAR MUSCLE AND NERVES 355 



The recent work of Bayliss (1901) on the origin of the vaso- 

 dilator nerves has confirmed and completed Strieker's observations, 

 although it is partly contradictory of the conclusions just 

 enumerated. Electrical, chemical, thermal, and above all mechanical 

 stimulation of the peripheral trunk of the divided posterior roots 

 of the fifth, sixth, and seventh lumbar, and the first sacral nerves, 

 determine on the dog a pronounced vaso-dilatation of the hind- 

 limb. A similar dilatation of the fore-limb is exhibited on 

 stimulating the posterior roots of the sixth, seventh, and eighth 

 cervical and first thoracic nerves. The dilator fibres of the hind- 

 limbs do not run with the abdominal sympathetic, but enter the 

 lumbo-sacral plexus direct. They degenerate after extirpation of 

 the spinal ganglia, but do not degenerate when the posterior roots 

 are cut between the cord and the spinal ganglia. They thus 

 behave in a manner perfectly analogous to all other nerve-fibres 

 emerging from the posterior roots, which have their trophic centres 

 in the spinal ganglia. Lastly, it has not been demonstrated that 

 the hind-limbs receive any vaso-dilator fibres other than those 

 which run in the posterior spinal roots. 



Till quite recently little was known of the dilator fibres to the 

 visceral vessels. Bradford, on methodically stimulating the several 

 pairs of spinal nerves with low frequency currents, found that the 

 eleventh, twelfth, and thirteenth dorsal pairs at least, in addition 

 to the constrictor fibres, contain numerous dilator fibres to the 

 renal vessels, these being, on the contrary, very few in the other 

 dorsal pairs, and altogether absent in the lumbar pairs. On 

 experimenting by the same method with the splanchnic, the most 

 important of the vaso-constrictor nerves, he found that it also 

 contains vaso-dilator fibres, which probably serve the intestines. 



After Eckhard's discovery of the nervi erigentes (1863) they 

 were at a later period studied by Gaskell (1887) and Morat (1890), 

 with the object more particularly of determining their origin. It 

 was found that stimulation of the anterior roots of the second and 

 third sacral nerves in rabbit, and first and second sacral nerves in 

 the dog, caused almost as pronounced an erection of the penis 

 as the stimulation of the nervi erigentes. Stimulation of the 

 posterior roots never produces the slightest trace of erection. 



These are the most important experimental data in regard to 

 the origin and course of the vaso- dilators. 



V. The vascular nerves, like the cardiac nerves, are capable of 

 reflex excitation, i.e. they can be stimulated by the afferent nerves 

 to the centres. As in the heart there are afferent nerves which 

 act reflexly upon the heart itself, -so in the vessels we must 

 assume the existence of afferent nerves, capable of acting reflexly 

 on the vessels. This was first demonstrated by Heger (1887). In 

 the curarised dog or rabbit he injected nicotine or silver nitrate, 

 peripherally, by the crural artery, and simultaneously recorded the 



