312 A MANUAL OF PHYSIOLOGY 



eighth hour no further trace of them was detected. About the 

 eighth hour they reappeared in the caecum, where they remained 

 with little or no onward movement till the fourteenth hour. 

 From the fourteenth to the sixteenth hour they travelled along 

 the ascending colon, and tarried a long time at the left angle of 

 the colon. From the nineteenth to the twenty-second or twenty- 

 fourth hour they slowly passed downward in the descending colon 

 and stopped at the sigmoid flexure, till their expulsion in defe- 

 cation. In some subjects the entire passage of the capsules was 

 complete in sixteen hours, in others not until after thirty hours. 



Vomiting. We have seen that under normal conditions the 

 movements of the alimentary canal always tend to carry the food 

 in one definite direction, along the tube from the mouth to the 

 rectum. The peristaltic waves generally run only in this direc- 

 tion, and, further, regurgitation is prevented at three points by 

 the cardiac and pyloric sphincters of the stomach and the ileo- 

 colic sphincter and valve. But in certain circumstances the 

 peristalsis may be reversed, one or more of the guarded orifices 

 forced, and the onward stream of the intestinal contents turned 

 back. In obstruction of the bowel, the faecal contents of the 

 large intestine may pass up beyond the ileo-caecal valve, and, 

 reaching the stomach, be driven by an act of vomiting through 

 the cardiac orifice ; in what is called a ' bilious attack,' the con- 

 tents of the duodenum may pass back through the pylorus and 

 be ejected in a similar way ; or, what is by far the most common 

 case, the contents of the stomach alone may be expelled. 



Vomiting is usually preceded by a feeling of nausea and a rapid 

 secretion of saliva, which perhaps serves, by means of the air 

 carried down with it when swallowed, to dilate the cardiac orifice 

 of the stomach, but may be a mere by-play of the reflex stimula- 

 tion bringing about the act. The diaphragm is now forced down 

 upon the abdominal viscera, first with open and then with closed 

 glottis. The thoracic portion of the oesophagus is thus placed 

 under diminished pressure, and therefore widened, while saliva 

 and air are aspirated into it out of the mouth. The abdominal 

 muscles strongly contract. At the same time the stomach itself, 

 and particularly the antrum pylori, contracts, the cardiac orifice 

 relaxes, and the gastric contents are shot up into the lax oeso- 

 phagus, and through it into the pharynx, and issue by the mouth 

 or nose. The movements of the stomach during vomiting induced 

 by apomorphine have been studied in the cat by the Rontgen ray 

 method. There is first observed extreme relaxation of the cardiac 

 end ; then a deep constriction appears a little below the cardiac 

 orifice, and runs towards the pylorus, increasing in depth as it 

 goes. When the transverse band is reached, this contracts 

 firmly and remains contracted, and the constriction passes on 



