THE AUTONOMIC NERVE SYSTEM 669 



spleen; and (b) to inhibit the tonus and dimmish the degree of contraction 

 of the muscle walls of the stomach and intestine; (c) to inhibit the tonus, 

 during digestion, of the sphincter muscle of the common bile duct; and (d) 

 to augment the tonus and degree of contraction of the muscle-walls of the 

 gall-bladder; (e) to augment the tonus of the ileo-colic sphincter muscle; (/) 

 to augment the secretion of the adrenal bodies. 



These effects are readily observed if the great splanchnic nerve is first 

 divided and then its peripheral end stimulated with induced electric currents. 

 With the division of the nerve the blood-vessels of the splanchnic area, as 

 well as of neighboring organs, dilate, attended by a sudden fall of the general 

 blood-pressure; with the beginning of the stimulation the blood-vessels of 

 the corresponding areas at once contract, coincident!^ with which there is a 

 rapid rise in the general blood-pressure. 1 The division of the splanchnics 

 is followed by a rise in the tonus of the muscle-walls of the intestine (due to 

 the augmentor activity of the now unopposed vagi nerves); stimulation of 

 the peripheral end of the splanchnics is followed by a marked inhibition of 

 the tonus. 



The functions of the lumbar fibers that terminate in the ganglia of the 

 same levels are: (a) To augment the tonus and the degree of contraction of 

 the blood-vessels of the skin of the trunk to which they are distributed; and 

 (b) to augment the activities of the sweat-glands of the corresponding regions. 



The functions of the nerve-fibers that cross the sympathetic chain and 

 unite to form the inferior splanchnic nerves, together with their ganglionic 

 continuations (the inferior mesenteric ganglion and the hypogastric plexus) , 

 are : (a) To augment the tonus and the contractile power of the blood-vessels 

 of the pelvic viscera; (b) to inhibit the tonus and diminish the contractile 

 power of the muscle-walls of the large intestine; (c) to augment the tonus of 

 the sphincter muscle of the urinary bladder, and to inhibit the tonus of the 

 muscle-walls of the bladder during the intervals of urination; (d) to augment 

 the tonus and contractile power of the uterus. 



These various phenomena arise when either the pre-ganglionic or the 

 post-ganglionic fibers in the hypogastric plexus are stimulated with induced 

 electric currents. 



The functions of the fibers which descend the sympathetic chain to ter- 

 minate around the cells of the lumbar and sacral ganglia are (a) to augment 

 the tonus and the degree of contraction of the blood-vessels of the skin of the 

 hip and leg; and (b) to augment the activities of the epithelium of the sweat- 

 glands of the corresponding parts. By reason of the distribution of the 

 visceral branches of the sacral ganglia a similar contraction of the blood- 

 vessels is observed in portions of the pelvic viscera and the external genitalia. 



The Functions of the Sacral Autonomic Nerves. The functions of the 

 pre-ganglionic nerve-fibers that leave the spinal cord by way of the ventral 

 roots of the second, third and perhaps the fourth sacral nerves, together with 

 their post-ganglionic continuations (the pelvic ganglia and their branches) 

 are: (a) To inhibit the tonus and cause a dilatation of the blood-vessels of 

 the generative organs; (b) to inhibit the tonus of the sphincter muscle of the 



1 Occasionally stimulation of the splanchnic is followed by a slight primary inhibition and dila- 

 tation of the blood-vessels which would lead to the inference that vaso-dilatator fibers are also 

 present; these fibers, however, do not belong properly to the autonomic system as their center of 

 origin is in the ganglia of the dorsal roots of the spinal nerves. 



