3 8o TEXT-BOOK OF PHYSIOLOGY 



The vaso-dilatator nerve-fibers that are found in some of the sacral 

 nerves have their origin in nerve-cells in the gray matter of the lumbar 

 or sacral region of the spinal cord. From these cells they pass into the ventral 

 roots of the second and third sacral nerves to be ultimately distributed by 

 way of the pelvic nerve to sympathetic ganglia in the pelvic region around 

 the cells of which their terminal branches arborize. From these ganglia 

 post-ganglionic fibers emerge which pass to the blood-vessels of the organs of 

 generation and adjacent structures. 



Antidromic Vaso-dilatator Nerve-fibers. Vaso-dilatator nerve-fibers 

 are associated with the vaso-constrictor fibers and are present in the trunks of 

 the spinal nerves and are distributed to the blood-vessels of the skin of the 

 limbs and trunk. Though it has been generally believed that these vaso- 

 dilatator fibers have their origin in nerve-cells in the ventral horns of the 

 gray matter, that they pass outward through the ventral roots of the thoracic 

 and lumbar nerves, that they belong to the efferent system of nerves, yet 

 these facts have never been positively determined. While this may be the 

 correct interpretation doubt has been thrown upon it by the investigations 

 of Bayliss. From the results of a long series of experiments this investigator 

 concludes that vaso-dilatator nerves for the regions of the body just men- 

 tioned, do not leave the spinal cord in the ventral roots; that the vaso-dilata- 

 tion observed on stimulation of the mixed spinal nerve is due to the presence 

 of nerve-fibers that do not differ from the ordinary afferent or sensor, posterior 

 or dorsal root fibers; that these nerve -fibers, moreover, have their origin in the 

 nerve-cells of the ganglia of the dorsal roots. From the fact that they trans- 

 mit nerve impulses to blood-vessels in a direction contrary to that of other 

 afferent nerve r fibers, the term antidromic has been given to them. The 

 centers from which they arise are capable apparently of being aroused to 

 activity by impulses transmitted to them from other regions of the body. 



These statements are based on the following facts: Stimulation of the 

 peripheral ends of the divided dorsal roots of the upper thoracic and lumbo- 

 sacral nerves gives rise to vascular dilatation in the upper and lower limbs; 

 separation from the cord is not followed by their degeneration, hence they 

 are not efferent nerves; extirpation of the ganglia of the dorsal roots is, 

 however, followed by their degeneration, hence their trophic centers are 

 in these ganglia. Whether the blood-vessels of the abdominal viscera which 

 apparently receive vaso-dilatator nerve impulses are supplied by nerves 

 having the foregoing origin and action, is a subject for further investigation. 



The course, distribution, and functions of the vaso-dilatator nerves have 

 been determined by the same methods as those employed in the investigation 

 of the vaso-constrictor nerves. Thus division and stimulation of the pe- 

 ripheral branches of the nerve of Wrisberg, e.g., the great petrosal and the 

 chorda tympani, is followed by an active dilatation of the blood-vessels of 

 the nasal chambers and palate, and of the blood-vessels surrounding the sub- 

 maxillary and sublingual gland. The inflow of blood is so great that the 

 submaxillary gland becomes bright red in color. Its tissues being unable 

 to consume all the oxygen, the blood emerges in the veins almost arterial 

 in color. Stimulation of Jacobson's nerve has the same effect on the blood- 

 vessels of the parotid gland. Stimulation of the branches of the sacral 

 nerves which collectively constitute the nervus erigens is followed by a dilata- 

 tion of the blood-vessels of the sexual organs. 



