408 OF FOOD, AND THE DIGESTIVE PROCESS. 



it, this was emptied of its contents, by the compression of the parietes of the 

 abdomen, when tartar emetic was injected into the veins. But this fact by no 

 means disproves the active co-operation of the stomach ; and judging from the 

 analogy of the uterus, bladder, and rectum whose muscular walls are all 

 actively concerned in the expulsion of their contents, though that expulsion is 

 in great part due to the contraction of the abdominal muscles we should be led 

 to concur with the common opinion, of which our own sensations during the act 

 would indicate the correctness. And this opinion has been confirmed by observ- 

 ation of a case, 1 in which the abdominal parietes having been accidentally laid 

 open in the human subject, and the stomach having wholly protruded itself, it was 

 seen to contract itself repeatedly and forcibly, during the space of half an hour, 

 until by its own efforts it had expelled all its contents except gases. As already 

 mentioned, the relaxation of the cardiac sphincter is essential to the act of 

 vomiting ; and unless this take place, all the other movements will be in vain ; 

 for its fibres, when contracted, can resist the combined force of all the expulsor 

 muscles. There can be little doubt that the violent but fruitless efforts at vomit- 

 ing which we occasionally witness (two or three such efforts frequently preceding 

 the effectual one), are prevented from emptying the stomach by the obstinacy with 

 which the cardiac sphincter is kept closed; just as the expiratory effort which 

 assists in emptying the stomach, is prevented, by the firmness with which the 

 glottis is held shut, from expelling the contents of the chest. It is not true, as 

 was formerly supposed, that the diaphragm actively co-operates in the effort of 

 vomiting ; for, as was first pointed out by Dr. M. Hall, 2 this effort, like those of 

 defecation, urination, and parturition, is essentially performed by the muscles of 

 expiration ; with this difference, however, that the diaphragm, instead of being 

 passive, is fixed, and supplies a firm surface against which the stomach is pressed. 

 In this, as in the other cases just referred to, the expulsive effort is preceded by 

 a deep inspiration, after which the glottis is spasmodically closed during its whole 

 continuance. The immediate causes of vomiting may be reduced to three dif- 

 ferent categories : 1st. The contact of irritating substances with the mucous 

 membrane of the stomach itself; these, however, cannot act upon more than its 

 muscular coat by direct stimulation ; and their operation upon the associated 

 muscles must take place by reflexion, through the " nervous circle" furnished 

 by the pneumogastrics and the motor nerves of expiration. 2d. Irritations 

 applied to other parts of the body, likewise operating by simply reflex transmis- 

 sion ; as in the vomiting which is consequent upon the strangulation of a hernia, 

 or the passage of a renal calculus; or in that which is excited by the injection of 

 tartar emetic or emetin into the circulating current, where these substances pro- 

 bably produce their characteristic effect by their operation on the nervous centres. 

 3d. Impressions received through the sensorial centres, which may be either 

 sensational or emotional, but which do not operate unless they are felt. In this 

 mode seems to be excited the vomiting that is induced by tickling the fauces, 

 which first gives rise to the sensation of nausea; as well as the vomiting conse- 

 quent upon disgusting sights, odors, or tastes, and upon those peculiar internal 

 sensations which are preliminary to " sea-sickness." The recollection of these 

 sensations, conjoined with the emotional state which they originally excited, may 

 itself become an efficient cause of the action, at least in individuals of pecu- 

 liarly irritable stomachs or of highly sensitive nervous systems; for this plays 

 downwards upon the sensorial centres, in such a manner as to excite in them 

 the same condition, as that which was originally produced through the medium 

 of the sensory nerve, when the object was actually present. (See CHAP. xiv. 

 SECT. 3.) 



1 Lepine in "Bullet, de 1'Acad. Roy. de Medecine," 1844. 

 8 "Quarterly Journal of Science," vol. xxv. p. 388, et seq. 



