212 DIGESTION. [CHAP. xxiv. 



stomach, which prevents or opposes the passage of the gastric con- 

 tents in that direction. Probably the whole of the pyloric third of 

 the stomach is strongly contracted under the circumstances which 

 ordinarily give rise to vomiting ; and the contents of the viscus 

 having been accumulated in its cardiac two-thirds, are thus brought 

 into more immediate and direct communication with the oesophagus. 

 The pylorus being closed against them, the stomach contents are 

 forced through the oesophagus, not only by the muscular contraction 

 of the stomach itself, but also by that of the abdominal muscles and 

 the diaphragm.* 



It is probable that where a very complete obstruction exists at or 

 near the pylorus, as in cases of hernia and other mechanical obstacles, 

 the act of vomiting partakes much of the nature of an overflow, 

 and requires no more than the action of the muscular coat of the 

 stomach itself. The slight effort which accompanies the discharge 

 of the stomach's contents in cases of this description, denotes this. 

 But when vomiting is caused by an emetic, or is the result of sea- 

 sickness, or of nervous irritation, as in stimulation of the fauces, 

 or in brain disease, an active, and almost convulsive, contraction 

 of the diaphragm and abdominal muscles accompanies it, and, 

 no doubt, constitutes the principal expelling force. These muscles 

 by the simultaneous forcible contraction form two plane surfaces, 

 one passing downwards and backwards, the other nearly vertically 

 downwards, which are approximated very closely to each other, 

 and compressing the stomach between them, cause the forcible 

 ejection of its contents in that direction, which offers least or no 

 resistance, namely, through the oesophagus. 



The act of vomiting is ushered in by a deep inspiration, during 

 which the diaphragm is firmly contracted. Just at this moment 

 the abdominal muscles contract forcibly and almost convulsively. 

 Thus an effort at expiration, in which, doubtless other muscles take 

 part, besides those of the abdominal walls, quickly succeeds the 

 act of inspiration. But the diaphragm does not become relaxed 

 as in ordinary expiratory efforts, because the air is only very par- 

 tially and slowly expelled. For, at the same time that the ab- 

 dominal muscles and the diaphragm are thrown into contraction, 

 those of the glottis are exerted to a like convulsive action, and 

 maintain a partially closed state of the glottis which resists the ex- 



* The power of returning portions of the food at will (rumination), which 

 some men have acquired, is effected by a strong voluntary contraction of the 

 pyloric muscle, and by expulsive efforts operating directly on the cardiac portion 

 of the stomach, which can thus expel its contents only in the upward direction. 



