584 NERVOUS SYSTEM. 



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

 stimulated there is no effect upon the liver ; but if the stimulus be applied 

 to the central ends, the glycogenic processes become exaggerated, and sugar 

 makes its appearance in the blood and in the urine. Bernard made a num- 

 ber of experiments illustrating this point, upon dogs and rabbits. The cur- 

 rent employed was generally feeble, and it was continued for five or ten min- 

 utes, two or three times in an hour. In some instances the stimulation was 

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

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

 impression conveyed to the nerve-centres through the pneumogastrics. The 

 inhalation of irritating vapors and of anaesthetics produces an increased gly- 

 cogenic action in the liver. 



The effects of irritating the floor of the fourth ventricle, by which tem- 

 porary diabetes is produced, have been considered in connection with the 

 glycogenic action of the liver. This effect is not due to a direct transmis- 

 sion of the irritation to the liver through the pneumogastrics, for the phe- 

 nomena are observed in animals upon which this operation has been per- 

 formed 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 sympa- 

 thetic going to the solar plexus have been divided. The operation, however, 

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

 interfere with the experiment in some other way than by the direct influence 

 of the nerves upon the liver. 



Influence of the Pneumogastrics upon the Stomach and Intestines. Lit- 

 tle or nothing is known with regard to the action of the pneumogastrics on 

 the spleen, kidneys and suprarenal capsules. The influence of these nerves 

 upon the stomach and intestine will be considered under the following heads : 



1. The effects of Faradization of the nerves. 



2. The effects of section of the nerves upon the movements of the stom- 

 ach in digestion. 



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



Effects of Faradization. The stomach contracts under stimulation of 

 the pneumogastrics in the neck, not instantly, but after the lapse of five or 

 six seconds (Longet). Longet explained some of the contradictory results 

 obtained by other observers by the fact that these contractions are very 

 marked during stomach-digestion, while they are wanting " when the stom- 

 ach is entirely empty, retracted on itself and in a measure in repose." Stim- 

 ulation of the splanchnic nerves, while it produces movements of the intes- 

 tines, does not affect the stomach. Judging from the tardy contraction of 

 the stomach and the analogy between the action of the pneumogastrics upon 

 this organ and the action of the sympathetic nerves upon the non-striated 

 muscular tissue, Longet assumed that the motor action of the pneumogas- 

 trics is due, not to the proper filaments of these nerves, but to filaments de- 

 rived from the sympathetic. 



