492 DIGESTION. 



passed round the part seized, so as to include a piece of about 

 half an inch in diameter. Finally, the wound in the stomach 

 and that in the abdominal wall are sewn up, and the animal 

 placed in a warm place for some hours. 



130. Influence of Nerves upon the Secretion of the 

 Stomach. The stomach, like the submixillary gland, has two , 

 secretions; one thin, watery, and acid the gastric juice proper ; 

 the other thick, tenacious and alkaline the gastric mucus. 

 The latter is secreted and accumulates on the surface of the 

 gastric mucous membrane during fasting, while the former is 

 only secreted when an irritant is applied to the inside of the 

 stomach. The irritant may be mechanical, e. f/., the friction 

 caused by food, or any firm or hard substance introduced into 

 the stomach, tickling with a feather, or rubbing with a glass 

 rod. The most active chemical irritants are alkalies, which 

 produce, even in very dilute solutions, an abundant secretion. 

 This continues even after the alkali has been neutralized by 

 the ijastric juice or washed away by a stream of water. The 

 saliva which is swallowed by the animal thus excites the se- 

 cretion of gastric juice. Other stimulants are alcohol, ether, 

 pepper, and cold water. When an irritant is applied, the gas- 

 tric in neons membrane, which is of a pale color, immediately 

 becomes red ; its vessels dilate those of the submaxillary gland,' 

 and the watery-looking gastric juice oozes rapidly from its 

 surface. The nerve centres, on which secretion is dependent, 

 are present in the walls of the stomach itself, for it takes place 

 even after all the nerves which enter the viscus from without 

 have been divided. These centres are, however, as we shall 

 see. much influenced by the vagi. 



The Action of the Vagus on the stomach is stilL much dis- 

 puted, hut it would appear from the experiments of Bernard 

 and Rutherford that it contains afferent fibres, the irritation of 

 which, as, e. g., during digestion, causes reflex dilatation of the 

 gastric vessels. Bernard found that section of the vagi during 

 digestion caused the stomach to become pale, and that in one 

 or more experiments, irritation of these nerves reddened it, and 

 inducei 1 an abundant secretion. He did not, however, deter- 

 mine whether this effect was due to afferent or efferent fibres, 

 but Rutherford found that, while section of the vagi during di- 

 gestion caused the stomach to become pale, irritation of their 

 central ends generally reddened it. This effect was, however, 

 sometimes preceded by its opposite, the organ becoming pale at 

 first ai.d afterwards red, a result which indicates that the vagus 

 contains two sets of afferent fibres, one of which increases, 

 while the other diminishes the degree of contraction of the gas-' 

 trie vessels. 1 



From the observation of Bernard and Blondlot, that gentle excita- 

 tion increases the secretion of gastric juice while violent irritation stops 



