PNEUMOGASTRIC, OR PAR VAGUM NERVE. 6G3 



looked for sugar in the blood and in the urine and did not confine his examinations to 

 the substance of the liver. 



After division of the pneumogastrics in the neck, if the peripheral ends be galvanized, 

 there is no effect upon the liver ; but, if galvanization be applied to the central ends, the 

 glycogenic function becomes exaggerated, and sugar makes its appearance in the blood 

 and in the urine. Bernard has made a number of experiments illustrating this point, 

 upon dogs and rabbits. The galvanic current employed was generally feeble, and it was 

 continued for from five to ten minutes, two or three times in an hour. In some instances 

 the irritation was kept up for thirty minutes. From these experiments, it is assumed that 

 the physiological production of sugar by the liver is reflex and is due to an impression 

 conveyed to the nerve-centres through the pneumogastrics. A very interesting and 

 adroit experiment by the same observer shows that section of the pneumogastrics be- 

 tween the lungs and the liver does not affect the production of sugar. This delicate 

 operation is performed by making a valvular opening in the chest, preventing the ingress 

 of air by suddenly forcing the finger into the wound, and then introducing a long, deli- 

 cate hook with a cutting edge, and dividing the nerves, which may be reached by the 

 finger in small dogs, and feel like tense cords by the side of the oesophagus. We have 

 already noted that the inhalation of irritating vapors and of anaesthetics produces a 

 hypersecretion of sugar by the liver. 



The remarkable effects of irritating the floor of the fourth ventricle, by which we 

 can produce temporary diabetes, have been considered fully in connection with the gly- 

 cogenic function of the liver. This effect is not due to a direct transmission of the irri- 

 tation to the liver through the pneumogastrics, for the phenomena of hypersecretion are 

 observed in animals upon which this operation has been performed after section of both 

 pneumogastrics in the neck. It is probable, indeed, that the impression is conveyed to 

 the liver through the -sympathetic system, for it has been shown that animals do not 

 become diabetic after irritation of the floor of the fourth ventricle, when the branches 

 of the sympathetic going to the solar plexus have been divided. The operation, how- 

 ever, of dividing the sympathetic nerves in this situation is so serious, that it may inter- 

 fere with the experiment in some other way than by the direct influence of the nerves 

 upon the liver. 



Influence of the Pneumogastrics upon tlie Stomach and Intestines. The number of 

 observations that have been made upon the influence of the pneumogastric nerves on 

 digestion in the stomach is immense, and many of the earlier experiments were quite 

 contradictory. "We do not propose, however, to treat of this subject from a purely his- 

 torical point of view, for the reason that, before 1842 and 1843, when gastric fistulee 

 were first established in living animals, little was known of the normal movements of the 

 stomach and of the mechanism of the secretion of the gastric juice ; and, farthermore, 

 before the observations of Bouchardat and Sandras, in 1847, the effects of section of the 

 nerves in the neck upon the action of the oesophagus in deglutition were not understood. 

 If we study the literature of the subject anterior to 1842, we find a great deal of confu- 

 sion, due to the facts just stated. Leaving out of the question most of the earlier ex- 

 periments, we shall treat of the influence of the pneumogastrics upon the stomach and 

 intestines, under the following heads : 



1. The effects of galvanization of the nerves. 



2. The effects of section of the nerves upon the movements of the stomach in digestion. 



3. The effects of section of the nerves upon the secretion of the gastric juice and the 

 chemical processes of digestion. 



4. The influence of the nerves upon the small intestine. 



Effects of Galvanization. As the result of recent experiments, the effects of galvan- 

 ization of the pneumogastrics upon the movements of the stomach are unquestionable. 

 Longet has shown that the stomach contracts as a consequence of irritation of the nerves, 

 not instantly, but after the lapse of five or six seconds. lie explains some of the contra- 



