may be rendered, as will now be shown, incapable of affording the required neutralizing power, by increasing beyond a certain point the strength of acidity of its contents. It has been already mentioned that, on arresting the circulation of the stomach whilst digestion is going on, the stomach yields as well as its contents. This yielding I have observed in the case of the rabbit to proceed to the extent of perforation; but in the dog it has only amounted to softening and solution of the mucous or internal coat-a circumstance that evidently depends upon the contents of the stomach being less powerfully acid in the dog than they are in the rabbit; for, on increasing their acidity before the circulation is stopped, digestion more actively proceeds, and soon gives rise to the occurrence of perforation. It is possible that some acid may be generated from the food in the stomach of the rabbit, as well as derived from the process of secretion; at all events, the strength of acidity of the contents of the stomach is conspicuously great in this animal. It has just been stated that if an acid be introduced into the stomach of the dog, and the circulation through its walls be stopped, digestion afterwards actively proceeds, and soon occasions perforation. A moderate amount of acid suffices for producing this result; and the dilute phosphoric and the citric are the acids I have employed in my experiments, that no corrosive action. should be exerted. In other experiments, where the same acids, in the same quantities, have been introduced into the stomach, and its circulation allowed to remain free, no digestion of its parietes has occurred. On proceeding further, however, but still without intro ducing a liquid that would act corrosively on the tissues, the stomach yields to solution, notwithstanding its circulation is left free. In an experiment where dilute hydrochloric acid was employed, perforation took place in an hour and forty minutes, and the stomach throughout was in an advanced state of digestion. A considerable amount of blood, it was found, had escaped from its vessels; and it will be remembered that considerable hæmorrhage was also remarked from the rabbit's ear as it was undergoing digestion in the dog's stomach. Thus, in one set of experiments, where a certain quantity of acid is introduced into the stomach, and the circulation of blood through its walls arrested, it is found to yield to digestion, because there is no neutralizing agency in operation to destroy the acidity— and thereby the activity-of the gastric juice tending to penetrate and act upon its texture. In another set of experiments, of precisely the same kind, except that the circulation is allowed to remain free, the stomach escapes, because the penetration of its walls by gastric juice in an acid and active state is prevented. In a third kind of experiment the circulation is again left free; but the quantity of acid is increased, and the stomach yields, because, as in the case of the rabbit's ear and frog's legs, the neutralizing capacity of the circulation is insufficient to overcome the acidity that is opposed to it. I look upon these results as in the highest degree confirmatory of the view that has been propounded. One point yet remains to be referred to before I dismiss the subject under consideration. It is incom patible with the view proposed that a living organism should be capable of existing in a free or isolated state in an actively digesting stomach, without yielding to attack, unless it should consist of, or be invested and protected by, an indigestible material. Now, it is well known as a veterinary fact, that larvæ of the Eustrus (bots) are sometimes met with in large numbers in the stomach of the horse; and it might appear, at first sight, that we have here an instance standing at variance with the proposition that has been laid down. It will be found, however, if attention be given to the point, that these larvæ do not live in an unattached state in the stomach. They exist with their mouths firmly attached to and buried in the inner coat; indeed, the inner surface of the stomach is often to be seen hollowed into a number of cells of a honeycomb nature, into which the larvæ, from the telescope-like construction of their bodies, can draw themselves so as almost to be concealed. Living upon the juices of the animal they infest, they also become more or less, as it were, a part and parcel of the stomach's parietes; and it is further to be remarked that the principle, chitine, which forms the basis of the external tunic of members of the insect tribe, is of an exceedingly indigestible nature. The indigestible character of the investment of these larvæ is shown by the fact that, after they become detached, they pass through the stomach and along the alimentary tract, without suffering loss of life, for they are found to be voided in a living state. Professor Simonds has informed me that he has met with an entozoon (a species of Filaria) which inhabits the last stomach of the sheep. This parasite, however, like the Eustrus, lives firmly attached to the mucous membrane; and I have not been able to learn that any example can be brought forward of an isolated digestible organism living in the healthily acting stomach without yielding to digestion. The older physiologists discovered, during their early experiments on digestion, that leeches and earthworms inserted into perforated metal spheres, and introduced in a living state into the digesting stomach, underwent digestion like morsels of ordinary food. I will now proceed to speak of the morbid phenomena connected with the action of the stomach. VOMITING. Vomiting constitutes a form of morbid action consisting of the rejection of the contents of the stomach by means of violent involuntary muscular efforts. The occurrence of the muscular efforts without any ejection taking place from the stomach constitutes what is known as retching. Although the act of vomiting cannot be regarded as forming one of the ordinary or natural events of life, yet, when excited by the presence of irritant or noxious matter in the stomach, it must be looked upon as constituting a most salutary process, leading, as it does, to the rejection of ingesta, which, if retained, would prove hurtful to the system. It may be compared in its object to the acts of sneezing and coughing-muscular phenomena effecting the expulsion of irritating matter from the respiratory passages. The act of vomiting is usually ushered in by a peculiar sense of uneasiness-a feeling of nausea, as it is termed. This is usually accompanied with more or less giddiness or faintness, coldness of the surface, pallor of the lips and face, dejection of countenance, and smallness, feebleness, and irregularity of pulse. As the act is about to be accomplished, the chest is filled with air by a long-drawn and often sonorous inspiration. The glottis being now closed, the violent muscular efforts that ensue exert a powerful compressing action upon |