The mechanical physiologists ascribed hun ger to the friction of the different parts of the internal membrane of the stomach on each other, an opinion which, although sanctioned to a certain extent by Haller,* must be aban doned, whether we regard the anatomical structure of the part, which shows that such friction is incompatible with its rounded form, and the disposition of its muscular fibres, or the nature of the sensation itself, which is specifically different from that produced by pressure, or any species of mechanical impulse on the surface of the body. Nor can the hy pothesis be maintained, which supposes that the action of the gastric juice, by its tendency to decompose organized substances, exercises a degree of this eroding quality on the internal coat of the stomach, and thus produces the uneasy sensation. But in this hypothesis the great distinction, which has been so frequently referred to, between living and dead matter as to the action of the gastric juice is disregarded; besides that from every analogy which we pos sess, it might be presumed that a substance so mild and apparently so little active as the gas tric juice, could not produce effects, which must be attributed to a body possessed of highly acid or noxious qualities. And it may be fur ther remarked, that in cases of the most pro tracted privation of food, and where death has occurred after the most severe pangs of hunger, nothing like erosion of the stomach has been observed, and that conversely, in those in stances where this effect has been produced after death, we have no reason to suppose that it was in any degree caused by the deficiency of food, or had been preceded by hunger.
From what has been stated above it may be inferred that the view which we feel disposed to take of the efficient cause of hunger is to regard it as a specific perception, occasioned by a peculiar state induced on certain of the nerves of the stomach, in the same way that certain nerves of the eye and of the ear receive the impressions of light and of sound. There is, however, this difference between the two cases, that in the instance of the eye and the car we arc able to point out the agent by which the impression is made, whereas we are unable to do this with respect to the stomach.* The perception of thirst, although seated in the tongue and fauces, is so intimately con nected with the state of the stomach, as to be properly referred to our consideration in this place. It is immediately produced by a defi ciency of the mucous secretion of the part, and consequently must be regarded as ulti mately depending on a peculiar condition of the glands which secrete this substance. Al though the sensation of thirst has a less specific character than that of hunger, yet we conceive that it must be referred to a peculiar action induced upon the nerves of the part, in a way analogous to what we suppose to take place with respect to hunger, and like it depending on a peculiar action, the intimate nature of which we are unable to explaimi There are various circumstances, which differ much in their nature and origin, acting upon different parts of the system, which all concur in producing a peculiar sensation termed nausea, which is referred to the region of the stomach. It is usually attended with a considerable derangement of all the powers of the body, both muscular and nervous, and if continued, produces the effort to vomit. The act of vomit ing consists in an inversion of the peristaltic motion of the stomach, commencing at the pylorus, which causes the contents to be carried towards the cardia, and to be forcibly ejected from the oesophagus. It has been generally supposed that the impression which produces nausea, and ultimately vomiting, is in the first instance made on the nerves of the stomach, that it is communicated by them to its muscu lar fibres, that their action is transmitted, probably by the intervention of the nerves, to the muscles of the abdomen and to the dia phragm, and that their contraction cooperates with the muscular coats of the stomach in the evacuation of its contents. It has long been a
subject of controversy among physiologists in what degree the abdominal muscles assist the coats of the stomach, or how far the latter are competent to produce the effect without the aid of the former. Haller supposed that the stomach alone is capable of evacuating its contents,* while Chirac, Duvemeyit and other French physiologists conceived that this organ is entirely passive in the act of vomiting, and the same opinion has been lately maintained by Magendie, and supported by a series of direct experiments. Ile not only found that vomiting was entirely suspended, when the abdominal muscles and diaphragm were ren dered incapable of acting upon the stomach, but he even informs us, that when the stomach was removed, and a bladder substituted in its place, vomiting was still induced.! But we are still disposed to believe that the commonly received doctrine is the correct one ; that the action commences in the muscular fibres of the stomach, and is materially assisted by the diaphragm and abdominal muscles. We rest our opinion on the analogy of the other hollow viscera, the uterus, the bladder, and the intestines, where the contraction commences in the organ itself; on the ante cedent probability, that as the agent which produces the effect is, in most cases, applied to the stomach, it must he supposed to act immediately upon it, and lastly on the mecha nical nature of the act of vomiting, which appears to be produced rather by a sudden and forcible contraction of the organ itself, than by any external pressure exercised upon it. We conceive also that this view of the subject is confirmed by the effect that succeeds to the division of the par vag-um ; it is asserted that when this nerve is divided vomiting can no longer take place, and as it is distributed principally over the stomach, so as to make it appear that this organ is its specific destination, we may presume that the incapacity for vomit ing depends upon the loss of power in the stomach. § With respect to the causes of nausea they may be reduced to two heads ; those that act immediately on the stomach, and those that act, in the first instance, on the system at large. Of the first class the most active in their opera tion are the medicinal substances which are specifically styled emetics, from their peculiar tendency to produce nausea and subsequent vomiting. Besides these certain kinds of food, or food of any description, if it remain in an undigested state, and various substances of an acrid or stimulating nature frequently produce nausea and vomiting. In the second class of causes we have to enumerate various circum stances, which act upon parts of the body, sometimes very remote from the stomach, but which, either by direct nervous communica tion, by sympathy, or association, produce the effect in question. One of the most powerful of these is the motion of a vessel at sea, giving rise to the well-known and most distressing sensation of sea-sickness, certain morbid affec tions of the brain, particular odours and flavours, renal and biliary calculi, hernia' or other affec tions of the intestinal canal, and lastly, certain causes which can act only through the medium of the mind or imagination. These various circumstances, although so extremely different in their nature and origin, agree in producing a similar efleet on the stomach, which may be explained by referring to the nervous com munications which exist between the organ and every part of the system, and more espe cially with the other abdominal viscera and the brain.*