230 GASTRIC DIGESTION. 



and regularity than the other vegetative processes, such as general assimila- 

 tion, circulation and respiration. 



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 pneumogastric has been the 

 more carefully studied, experiments upon the sympathetic being more diffi- 

 cult. Although the complete history of the influence of the pneumogastrics 

 upon digestion belongs to the physiology of the nervous system, it will be 

 useful 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. 



The experiments of Bernard and others have shown that the vascular 

 mechanism of the mucous membrane is to a great extent under the influence 

 of the pneumogastrics. If these nerves be divided while gastric digestion is at 

 its height, the mucous membrane immediately becomes pale, and the secre- 

 tion of gastric juice is nearly if not quite arrested. It has been found, how- 

 ever, that gastric juice may be secreted in small quantity under the stimulus 

 of food, even when both pneumogastrics and the sympathetic nerves going 

 to the stomach have been divided (Heidenhain). 



Section of both pneumogastrics, while it does not entirely paralyze the 

 muscular coat of the stomach, renders its contractions irregular and feeble. 

 It is stated that section of these nerves is followed by " a short temporary 

 contraction of the cardiac aperture " (Stirling). 



Movements of the Stomach. As the articles of food are passed into the 

 stomach by the acts of deglutition, the organ gradually changes its form, 

 size and position. When the stomach is empty, the opposite surfaces of its 

 lining membrane are in contact in many parts and are thrown into longitu- 

 dinal folds. As the organ is distended, these folds are effaced, the stomach 

 itself becoming more rounded, and as the two ends, with the lesser curva- 

 ture are comparatively immovable, the whole organ undergoes a movement 

 of rotation, by which the anterior face becomes superior and is applied to 

 the diaphragm. At this time the great pouch has nearly filled the left hypo- 

 chondriac region ; the greater curvature presents anteriorly and comes in con- 

 tact with the abdominal walls. Aside from these changes, which are merely 

 due to the distention, the stomach undergoes important movements, which 

 continue until its contents have been dissolved and absorbed or have passed 

 out at the pylorus; but while these movements are taking place, the two 

 orifices are guarded, so that the food shall remain for the proper time exposed 

 to the action of the gastric juice. By the rhythmical contractions of the 

 lower extremity of the oesophagus, regurgitation of food is prevented ; and 

 the circular fibres, which form a thick ring at the pylorus, are constantly 

 contracted, so that at least during the first periods of digestion only 

 liquids and that portion of food which has been reduced to a pultaceous 

 consistence can pass into the small intestine. It is well known that this 

 resistance at the pylorus does not endure indefinitely, for indigestible articles 



