652 PHYSIOLOGY OF DIGESTION AND SECRETION. 



during the act. On the contrary, it may exhibit contractions, more 

 or less violent in character. According to Openchowski,* the 

 pylorus is closed and the pyloric end of the stomach firmly con- 

 tracted so as to drive the contents toward the dilated cardiac por- 

 tion. Cannon states that in cats the normal peristaltic waves pass 

 over the pyloric portion in the period preceding the vomiting and 

 that finally a strong contraction at the "transverse band" com- 

 pletely shuts off the pyloric portion from the body of the stomach, 

 which at this time is quite relaxed. The act of vomiting is, in fact, 

 a complex reflex movement into which many muscles enter. The 

 following events are described : The vomiting is usually preceded by 

 a sensation of nausea and a reflex flow of saliva into the mouth. 

 These phenomena are succeeded or accompanied by retching move- 

 ments, which consist essentially in deep, spasmodic inspirations with 

 a closed glottis. The effect of these movements is to compress the 

 stomach by the descent of the diaphragm, and at the same time to 

 increase decidedly the negative pressure in the thorax, and therefore 

 in the thoracic portion of the esophagus. During one of these 

 retching movements the act of vomiting is effected by a convulsive 

 contraction of the abdominal wall that exerts a sudden additional 

 strong pressure upon the stomach. At the same time the cardiac 

 orifice of the stomach is dilated, possibly by an inhibition of the 

 sphincter, and according to the above description the fundic end, 

 of the stomach is also dilated, while the pyloric end is in strong 

 contraction. The stomach contents are therefore forced violently 

 out of the stomach through the esophagus, the negative pressure in 

 the latter probably assisting in the act. The passage through the 

 esophagus is effected mainly by the force of the contraction of the 

 abdominal muscles; there is no evidence of antiperistaltic move- 

 ments on the part of the esophagus itself. During the ejection of 

 the contents of the stomach the glottis is kept closed by the adductor 

 muscles, and usually the nasal chamber is likewise shut off from the 

 pharynx by the contraction of the posterior pillars of the fauces on 

 the palate and uvula. In violent vomiting, however, the vomited 

 material may break through this latter barrier and be ejected 

 partially through the nose. 



Nervous Mechanism of Vomiting. That vomiting is a reflex act 

 is abundantly shown by the frequency with which it is produced in 

 consequence of the stimulation of sensory nerves or as the result 

 of injuries to various parts of the central nervous system. After 

 lesions or injuries of the brain vomiting often results. Disagreeable 

 emotions and disturbances of the sense of equilibrium may produce 

 the same result. Irritation of the mucous membrane of various 

 parts of the alimentary canal (as, for example, tickling the back 

 * " Archiv f . Physiologic, " 1889, p. 552. 



