ACTION OF THE MUSCLES IN VOMITING. 519 



animal, or its injection into the veins, was said, by Magendie, never to 

 produce contraction of the stomach. He found that, on drawing this 

 organ out of the abdomen, no vomiting occurred ; but, as soon as it 

 was replaced in its normal situation, the action of the abdominal mus- 

 cles, or the pressure of the hand, immediately produced vomiting; even 

 after removal of the abdominal muscles, so as to leave only the linea 

 alba, or the tendinous structure in the middle line of the abdominal 

 walls, the descent of the diaphragm, according to that observer, still 

 emptied the stomach. Moreover, on removing the stomach, and sup- 

 plying its place by a bladder attached to the oesophagus, the contents 

 of the former were forced upwards by the contraction of the abdom- 

 inal muscles. It is, however, generally believed, that these experi- 

 ments merely prove, that the abdominal muscles are powerful agents 

 in expelling the contents of the stomach into the oesophagus, just as 

 they assist, most materially, in the expulsion of the contents of the 

 other hollow viscera. They do not show a completely passive condi- 

 tion of the stomach itself, which organ, as just stated, has been seen 

 to be able to empty its own contents. In experiments on animals, 

 when the abdomen is opened, the movements of the stomach are fre- 

 quently so feeble and rapid, that they might escape observation. 



It was supposed by Magendie that the diaphragm is actively con- 

 cerned in vomiting, undergoing a movement of deacent; but, the asso- 

 ciated acts necessary to vomiting are expiratory, and the descent of 

 the diaphragm is an inspiratory movement (Marshall Hall). At the 

 moment of vomiting, the diaphragm, though more or less contracted, 

 is certainly fixed ; for, previous to each act of vomiting, a powerful in- 

 spiratory effort occurs, and the diaphragm of course descends ; but the 

 glottis is then closed, and any further movement, on the part of the 

 diaphragm, is thus prevented, so that it probably remains passive in 

 vomiting. 



During vomiting, as in the second stage of deglutition, certain mus- 

 cles draw the soft palate across the pharynx, and prevent the vomited 

 substances from passing into the posterior nares; but when the abdom- 

 inal muscles act very powerfully, these are sometimes ejected through 

 the nose. 



As elsewhere mentioned, vomiting is a reflex act, the pneumogastric 

 nerves being the afferent nerves, the medulla oblongata and cord the 

 excitable centres, and the nerves of the various muscles concerned, 

 the efferent nerves. Sometimes it is exeito-motor, and induced by a 

 local stimulus, applied to the interior of the stomach itself, such as in- 

 digestible food, medicines, poisons, or diseased secretions ; it may also 

 be due to morbid irritability of this organ, from inflammation, ulcera- 

 tion, or other disease ; or the cause of irritation may be distant, as in 

 the intestines or some other part. In certain cases, as in sickness 

 produced by a blow on the eyeball or on the shin, by strangulation 

 of the intestine, or by a calculus in the kidney, the reflex act is sensori- 

 motor, or accompanied by sensations which are always of a painful 

 kind. The nausea and vomiting caused by tickling the fauces, by dis- 

 agreeable tastes and odors, or by sickening sights, are likewise sensori- 

 motor in their character. Sea-sickness is also an example of sensori- 



