252 DIGESTION. 



Influence of the Nervous System on the Stomach. It is well known that mental 

 emotions frequently have a marked influence on digestion, and this, of course, can take 

 place only through the nervous system. Of the two nerves which are distributed to the 

 stomach, the pnetimogastric has been the more carefully studied, experiments upon the 

 sympathetic being difficult and unsatisfactory. Although the complete history of the 

 influence of the pueumogastric nerves upon digestion belongs to the section on the nervous 

 system, it will be interesting in this connection to consider briefly some of the facts 

 which have been ascertained with regard to the influence which these nerves exert upon 

 the stomach. 



After section of the pneumogastric nerves in the neck, acts of deglutition are apparent- 

 ly performed, but the food usually collects in and distends the paralyzed oesophagus and 

 does not pass to the stomach. It is not surprising, therefore, that the first experiments 

 upon the influence of the pneumogastrics on digestion should have been contradictory, some 

 contending that section of the nerves arrested stomach-digestion, while others maintained 

 that the nerves had little or no influence upon the stomach. It is evident that, without 

 an appreciation of the effects of section of the pneumogastrics upon deglutition, observa- 

 tions on the influence of their section upon stomach-digestion would be of little value. 



The experiments of Longet seem to show that, while section of the pneumogastrics in 

 the neck undoubtedly diminishes the secretion of gastric juice, the production of this fluid 

 is not entirely arrested. He states that in dogs, one or two days after section of the 

 nerves, he found the lacteals filled with chyle after milk had been passed into the stom- 

 ach ; but it is now well known that chyle is in great part, if not entirely formed in the 

 intestinal canal, without the intervention of the stomach. Another experiment, however, 

 is more interesting. After section of the pneumogastrics, having exposed the mucous 

 membrane of the stomach, he found that an acid fluid appeared in parts which were sub- 

 jected to mechanical or galvanic irritation. The general results of his experiments on 

 this subject were that, after the division of both pneumogastric nerves, small quantities of 

 food could be digested in the stomach, but that a considerable mass was only chymitied 

 on the surface, the centre not undergoing any alteration. This he attributes, not so much 

 to arrest of secretion of the gastric juice, as to paralysis of the movements of the stomach, 

 which, when the mass of food is considerable, are necessary in order to expose all parts 

 to the action of the gastric juice. 



The experiments of Bernard on this subject are very clear and satisfactory. When 

 the mucous membrane of the stomach was turgid with blood, the animal (a dog) being in 

 full digestion and provided with a large gastric fistula so that the changes which might 

 take place in the stomach could be readily observed, the pneumogastrics were divided in 

 the neck. At once the mucous membrane became pale and flaccid, and the secretion of 

 gastric juice was arrested. When the animal died after section of the pneumogastrics 

 during digestion, it was remarked that the absorption of chyle seemed to have been ar- 

 rested, the lacteals being found to contain coagulated chyle even as far as the villi of the 

 intestines. According to these experiments, the action of gastric juice which might exist 

 in the stomach at the time of section of the pneumogastrics would continue, but no new 

 fluid is secreted ; and, if the fluid thus remaining in the stomach be neutralized, digestion 

 is immediately arrested. In one experiment in which the pneumogastrics had been 

 divided, having previously emptied the stomach, Bernard introduced meat finely divided. 

 The next day, the meat had a distinctly-ammoniacal odor and an alkaline reaction, the 

 result of spontaneous decomposition. These experiments show only an immediate arrest 

 of the secretion of the gastric juice. In certain exceptional instances, in which animals 

 survive the section of both nerves for a number of days or sometimes even recover, it 

 has been noted that, after a few days, an acid secretion again takes place in the stomach. 



Although much confusion exists in the earlier observations on the effects of section of 

 the pneumogastrics upon the stomach, the conclusions to be drawn from recent experi- 

 ments are tolerably definite. 



