662 NERVOUS SYSTEM. 



The above formulated statements express the experimental facts at present known 

 with regard to the influence of the pneumogastrics upon respiration. The pulmonary 

 branches themselves are so deeply situated that they have not as yet been made the sub- 

 ject of direct experiment, with any positive and satisfactory results. 



Properties and Functions of the (Esophageal Nerves. The muscular walls and the 

 mucous membrane of the oesophagus are supplied entirely by branches from the pneumo- 

 gastrics. The upper portion is supplied by filaments from the inferior laryngeal branches, 

 the middle portion, by filaments from the posterior pulmonary branches, and the inferior 

 portion receives the cesophageal branches. These branches are both sensory and motor; 

 but probably the motor filaments largely predominate, for the mucous membrane, although 

 it is sensible to the extremes of heat and cold, the feeling of distention, and a burning 

 sensation upon the application of strong irritants, is by no means acutely sensitive. 



That the movements of the oesophagus are animated by branches from the pneumo- 

 gastrics, has been clearly shown by experiments. In the first place, except in animals in 

 which the anatomical distribution of the nerves is different from the arrangement in the 

 human subject, the entire oesophagus is paralyzed by dividing the nerves in the neck. 

 When the pneumogastrics are divided in the cervical region, in dogs, if the animals 

 attempt to swallow a considerable quantity of food, the upper part of the oesophagus is 

 found enormously distended. Bernard noted in a dog in which a gastric fistula had been 

 established, that articles of food given to the animal did not pass into the stomach, although 

 he made great efforts to swallow. An instant after the attempt, the matters were 

 regurgitated, mixed with mucus, but of course did not come from the stomach. 



Direct experiments upon the roots of the pneumogastrics have shown that these 

 nerves influence the movements of the oesophagus, and that the motor filaments involved 

 do not come from the spinal accessory ; but it is not known from what nerves these 

 motor filaments are derived. 



Properties and Functions of the Abdominal Branches. In view of the very extensive 

 distribution of the terminal branches of the pneumogastrics to the abdominal organs, it 

 is evident that the functions of these nerves must be very important, particularly since 

 it has been shown that the right nerve is distributed to the whole of the small intestine. 

 We shall consider the functions of these branches in their relations to the liver, the 

 stomach, and the intestines. We have no positive information with regard to their action 

 upon the spleen, kidneys, and suprarenal capsules. 



Influence of the Pneumogastrics upon the Liver. There is very little known with regard 

 to the influence of the pneumogastrics upon the secretion of bile ; and the most important 

 experiments upon the innervation of the liver relate to its glycogenic function. We 

 shall have little to say upon this subject, however, in addition to what we have already 

 stated in treating of the liver as a sugar-producing organ. The view which we have 

 advanced with regard to the glycogenic function is that the liver is constantly producing 

 sugar during life, which is completely washed out by the blood in its passage through 

 this organ, the liver itself containing little or no sugar, under normal conditions. With 

 this view, we are to look for sugar in the blood in certain situations, and not in the liver 

 itself ; although, after death, a change of the glycogenic matter in the liver into sugar 

 takes place with great rapidity, and sugar may then be found in its substance. Normally, 

 sugar disappears in the lungs and is not found in the blood of the arterial system. The 

 presence of sugar in the urine is abnormal. If both pneumogastrics be divided in the 

 neck, and the animal be killed at a period varying from a few hours to one or two days 

 after, the liver contains no sugar, under the conditions in which it is generally found, 

 viz., a certain time after death. From experiments of this kind, Bernard concludes that 

 the glycogenic function is suspended when the nerves are divided. The experiments, 

 however, made by irritating the pneumogastrics, were more satisfactory, as in these he 



