572 THE MECHANISM OF THE ACT OF VOMITING. 
stomach had entirely passed through a wound of the diaphragm 
into the thorax, and in which it could not, consequently, be sub- 
jected to the action of that muscle. In some experiments, vomiting 
was observed also to take place, although the diaphragm had been 
paralysed by a division of the phrenic nerves, or its influence 
subtracted by a division of its anterior attachments. 
This view of the subject is still farther confirmed by facts I now 
proceed to state, which prove that the act of vomiting is an effort, 
not of inspiration, but of expiration. This is obvious enough on a 
mere observation of the states of the thorax and abdomen during 
vomiting. The larynx is evidently abruptly and forcibly closed, 
the thorax drawn downwards, and the abdomen inwards. 
Such, indeed, appears to me to be the precise nature of the act 
of vomiting, in ordinary circumstances. The contents of the thorax 
and abdomen are subjected to the sudden and almost spasmodic 
contraction of all the muscles of expiration, the larynx being closed 
so that no air can escape from the chest, and the two cavities 
being made one by the floating or inert condition of the diaphragm. 
The mere mechanism of the act of vomiting differs little, there- 
fore, from that of coughing, by which, indeed, the contents of the 
stomach are frequently expelled: the larynx in the former is, 
however, permanently, in the latter only momentarily closed ; and 
there is, doubtlessly, a different condition of the cardiac orifice and 
of the msophagus. 
It appeared to me from these views of the subject, that if an 
opening were made into the trachea, or through the parietes of the 
thorax, the effort of expiration constituting the act of vomiting 
would issue in expelling the air through these orifices respectively, 
and the evacuation of the stomach would be prevented. Therefore, 
determined to submit the fact to the test of experiment, I took a 
little dog, made an ample opening into the windpipe, and gave a 
few grains of the sub-sulphate of mercury. The animal soon became 
sick. The first efforts to vomit induced a forcible expulsion of 
air through the orifice in the trachea. These efforts soon be- 
came very violent, however, and the stomach at length yielded 
part of its contents. It was perfectly evident that the violent con- 
tractions of the abdominal muscles pressed upon the viscera of the 
abdomen, so as to carry the diaphragm upwards to its fullest 
extent, and at this moment vomiting was effected. The act of 
expiration was so forcible that a lighted candle placed near the 
tracheal orifice was several times extinguished. In a second ex- 
periment a free opening was made into the thorax between the 
sixth and seventh ribs of the right side : the lungs collapsed partially 
only. During the first efforts to vomit, air was forcibly expelled 
through this orifice, the lung was brought almost into contact with 
