MOVEMENTS OF THE STOMACH. 23 1 



contents glide to and fro with a slow rubbing movement. Such movements seem 

 to occur periodically, every period lasting several minutes {Beaumont). By these 

 movements the contents are moistened with the gastric juice, while the masses of 

 food are partly broken down. The formation of hair-balls in the stomach of dogs 

 and oxen indicates that such rotatory movements of the contents of the stomach 

 take place. (2) The other kind of movement consists in a periodically occurring 

 peristalsis, whereby, as with a push, the first dissolved portions of the contents of 

 the stomach are forced into the duodenum. They begin after a quarter of an hour, 

 and recur until about five hours after a meal. This peristalsis is most pronounced 

 towards the pyloric end, and the muscles of the pyloric sphincter relax to allow the 

 contents to pass into the duodenum. According to Eiidinger, the longitudinal 

 muscular fibres, when they contract, especially when the pyloric end is filled, may 

 act so as to dilate the pylorus. 



Gizzard. The strongly muscular walls of the stomach of grain-eating birds effect a tritura- 

 tion of the food. The older physiologists found that glass balls and lead tubes, which could 

 be compressed only by a weight of 40 kilos. , were broken or compressed in the stomach of 

 a turkey. 



Influence of Nerves. [The stomach is supplied by the vagi and by the sympa- 

 thetic, the right vagus being distributed to the posterior surface, and the left to the 

 anterior surface, of the organ.] Auerbach's ganglionic plexus of nerve-fibres and 

 nerve-cells, which lies between the muscular coats of the stomach, must be regarded 

 as its proper motor centre, and to it motor impulses are conducted by the vagi. 

 Section of both vagi does not abolish, but it diminishes the movements of the 

 stomach. The muscular fibres of the cardia may be excited to action, or their 

 action inhibited by fibres which run in the vagus (Nn. constrictores, et dilatator 

 cardiae). [If the vagi be divided in the neck, there is a short temporary spasmodic 

 contraction of the cardiac aperture. On stimulating the peripheral end of the vagus 

 with electricity, after a latent period of a few seconds, the cardiac end contracts, 

 more especially if the stomach be distended, but the movements are slight if the 

 stomach be empty. In curarised dogs, the pylorus contracts w r ith varying inten- 

 sity, and irregularly whether the vagi and splanchnics be intact or divided. 

 Stimulation of the vagi in the neck causes contraction of the pylorus, when the 

 latent period may be seven seconds. Stimulation of the splanchnics in the thorax 

 arrests the spontaneous pyloric contractions, the left splanchnic being more active 

 than the right (Oser).] 



Local electrical stimulation of the surface of the stomach causes circular constrictions 

 of the organ, which disappear very gradually, while the movement is often propagated to 

 other parts of the gastric wall. When heated to 25 C, the excised empty stomach exhibits 

 movements. Injury to the pedunculi cerebri, optic thalamus, medulla oblongata, and even to 

 the cervical part of the spinal cord, according to Schiff, causes paralysis of the vessels of certain 

 areas of the stomach, resulting in congestion and subsequent haemorrhage into the mucous 

 membrane. [It is no uncommon occurrence to find haemorrhage into the gastric mucous mem- 

 brane of rabbits, after they have been killed by a violent blow on the head.] 



[Action of Drugs. The automatic centres are excited by emetin, apomorphin, tartar emetic, 

 while. muscarin causes general contraction of the stomach. The activity of the automatic centres 

 is diminished by chloral, urethan, morphin, and nicotin, while atropin causes paralysis of the 

 nerve-endings (E. Schiitz).] 



158. VOMITING. Mechanism. Vomiting is caused by contraction of the 

 walls of the stomach, the pyloric sphincter being . closed. It occurs most readily 

 when the stomach is distended (dogs usually greatly distend the stomach by 

 swallowing air before they vomit) ; it readily occurs in infants, in whom the 

 cul-de-sac at the cardia is not developed. It is quite certain that in children 

 vomiting occurs through contraction of the walls of the stomach, without the 

 spasmodic action of the abdominal walls. When vomiting is violent, the 

 abdominal muscles act energetically. [The act of vomiting is generally preceded 

 by a feeling of nausea, and usually there is a rush of saliva into the mouth, 



