The Visceral or Splanchnic Division 101 



in one of the lateral or collateral ganglia, to a number of cells therein, 

 and its distribution in the tissues reached by the axons of these cells 

 thereby increased. The current transmitted through a single white ramus 

 is in many cases returned through the gray rami of many spinal nerves, 

 and passes along fibers in the nerves to many portions of the body. It is ' 

 not impossible that, conversely, afferent currents from a relatively large 

 area may be collected in one of these ganglia by the dendritic branches of 

 a single spinal ganglion cell. On this point, however, definite information 

 is not at hand. 



THE STIMULATION OF AFFERENT VISCERAL NEURONS. 



The excitability of the afferent neuron terminations in the walls of the 

 alimentary canal, especially the terminations of the visceral afferent neurons 

 belonging to the central nervous system, has long been a subject for study 

 and speculation. For a long time it was believed that these terminations, 

 at least those below the gullet, although afferent were not sensory, i. e., 

 that no consciousness could be produced or mediated through their 

 activity. It was shown that no specific sensations were experienced by a 

 patient when his intestines were handled, pressed upon, cut, electrically 

 stimulated, or even torn or burned. The peritoneal membrane covering 

 the intestine, and lining the abdominal cavity, were found sensitive in one 

 particular, i. e., ' pain ' was produced by strong stimulation ; but no con- 

 sciousness seemed to follow any operation on the intestines themselves. 



The pain of colic and other less acute discomfort localized in the ab- 

 dominal cavity were concluded to be due to peritoneal irritation. 



Later and more adequate experiments have shown, however, that certain 

 afferent currents from the intestines do produce consciousness, but that 

 these afferent currents are initiated only when the nerve terminals are 

 stimulated adequately, that is, in this case, when the intestinal muscular 

 fibers are contracted or stretched. Thus we derive the experiences of pain 

 (as of colic). Hunger "pangs" are due to contraction of the stomach; 

 fullness to stretching of the stomach walls ; and probably feelings of 

 ' faintness ' and satisfaction, and others not readily named, are due to 

 other variations in the stimulation of these organs. Chemical stimulation, 

 both by products of general metabolism and by hormones, are undoubtedly 

 of great importance in the arousal of consciousness of visceral conditions — 

 conditions which constitute a large part of emotions. 



Terminals of the local systems (of Auerbach and Meissner) are excitable 

 through pressure of the contents of the canal on the lining membrane, and 

 through the chemical substances contained in food, and in secretions of 

 other regions of the canal. In this way the internal control of the diges- 



