THE AUTONOMTC NERVOUS SYSTEM 885 



ergotoxine, however, a reversed effect is observed; namely, inhibition 

 instead of augmentation. By taking advantage of this fact, Dale has 

 been able to demonstrate in the hypogastric nerves inhibitory fibers to 

 the uterus, and Elliott has demonstrated the inhibitory action of epi- 

 nephrine on the muscles of the ureter in the dog. Inhibitory fibers have 

 also been discovered by these methods in the great splanchnic nerves, in 

 the nerve roots supplying the kidney, and in the cervical sympathetic 

 supplying the blood vessels of the mucous membrane of the mouth, etc.; 

 that is, in nerve trunks which previously were believed to contain only 

 augmentory fibers. The accompanying diagram from Jackson will give 

 an idea of the currently accepted views concerning the distribution of 

 augmentory and inhibitory fibers. (Fig. 233.) 



THE AFFERENT FIBERS OF THE AUTONOMIC SYSTEM 



It has long been known that the exposed viscera are remarkably insen- 

 sitive. This experience is in accord with the observation that the supply 

 of afferent fibers to the viscera is relatively very small. In the hypo- 

 gastric and probably in the great splanchnic nerve, Langley computes 

 that only about one-tenth of the medulla ted fibers are afferent. At the 

 two ends of the alimentary canal, where cooperative reflexes between 

 the somatic musculature and the viscera are of importance, a greater 

 number of afferent fibers are found in the autonomic nerves; for ex- 

 ample, in the pelvic nerve about one-third of the fibers are afferent, and, 

 as we have frequently seen, the vagi contain large numbers of them 

 coming from the lungs, stomach, and no doubt from other viscera. 



The afferent visceral fibers, as above stated, arise like those of the 

 voluntary system, from the ganglion cells of the posterior roots. They 

 travel in company with the connector fibers through the white ramus 

 communicans, so that the stimulation of the central end of one of these 

 may cause reflex rise in blood pressure and other movements. 



It is found that, after opening the abdominal cavity under local 

 anesthesia, cutting and suturing of the viscera may be continued without 

 causing any pain. When the viscera are inflamed, however, and under 

 certain conditions of stimulation, such as the distention of the bile ducts 

 with biliary calculi, or the violent contraction of the intestines, excruci- 

 ating pain may be evoked. This pain is frequently not localized in the 

 viscera, but is referred to certain parts of the surface of the body, and 

 it has been shown by Mackenzie and by Head that it is referred to the 

 area of skin which is supplied with sensory nerves by the same segment 

 as that to which the afferent autonomic fibers' of the particular viscus 

 run. It has further been shown that vascular disease may cause sensi- 



