Dr. Gosse, who could vomit at will, made also some valuable observations.

We owe, however, nearly all our knowledge on the subject to the following cases: 1. Alexis St. Martin, a Canadian boatman, in whom there existed a large gastric fistula, the result of a gun-shot wound. Dr. Beaumont most ably investigated this case, obtained gastric juice, and observed the action of food on the stomach, and of the stomach on food. 2. Catherine Kütt, aged 35 years, who had a gastric fistula opening between ninth and tenth left costal cartilages, from which Schmidt obtained 31 tb of gastric juice daily, of which 100 parts were required to dissolve 2 parts of albumen. Lehmann calculated the daily amount at from 60 to 80 ozs., as we ingest daily 3 or 4 ozs. of pure albumen, and finding that 5 parts are dissolved by 100 parts of that fluid. The amount of gastric juice is proportional to the wants of the system, not to the quantity of food taken a most important principle in dietetics, as any surplus must remain undigested, and in many feverish states none is secreted if food be taken. It is a colourless, slightly viscid fluid, with a sour smell and intensely acid reaction, specific gravity of 1.0023, and the following composition:

The pepsin and acid may be regarded as a conjugated acid the pepso-hydrochloric. There is probably much more acid, as in these analyses saliva and other alkaline matters may have neutralised a large amount. That the acid is hydrochloric is probable from the necessity there exists for the use of common salt, which would

afford this acid for the gastric juice and soda for the bile; it has been surmised that the pepsin may separate them. The fact that hydrochloric acid is the most highly diffusible of substances may have some connexion with its presence in the gastric juice. The presence of lactic acid was first stated in 1823 by our illustrious countryman, the late Dr. Graves, and since by Berzelius, and was obtained in 1856 from Alexis St. Martin, who has again submitted to experiment. Blondlot asserts that biphosphate of lime, and no free acid, exists-a view disproved by the fact that gastric juice, if heated with zinc, evolves hydrogen, whereas a solution of acid phospate will not. No mixture, however, of acids will digest alimentary matters without the aid of great and prolonged heat; but this necessity for high temperature is removed by the active principle, pepsin. This is contained in the dried mucous membrane of the fourth stomach of the calf, which is known as rennet, and was isolated therefrom by Wasmann. It acts as a ferment, being probably a protein body undergoing decay, and produces some catalytic effect on albuminous food, putrefaction being checked by the presence of the acid, for an artificial digesting fluid made from pepsin, without acid, putrifies.

Gastric juice acts mainly on the albuminoids, changing them into "peptone," which is identical, though derived from meat, cheese, albumen, &c. This substance, alluded to by Prout as "incipient albumen," is not coagulated by heat or nitric acid, and is much more soluble, and thus more easily absorbed through coats of vessels. Peptone does not give the red colour by Millon's test, but is thrown down by alcohol and bichloride of mercury, and has the effect of interfering with such chemical reactions, as the blue colour of starch with iodine, the reduction of oxide of copper by sugar, as in Trommer's test, &c. No great chemical change occurs in the production of peptone, as no gas is evolved, and the amount

of sulphur is the same as in albuminoids. It is probable that peptone is but a crystalloid form of albumen, that substance, by a change from its colloid condition, being readily diffusible through the coats of the stomach and the superimposed layer of mucus. Milk introduced into stomach is at once curdled, its casein being then converted into peptone; if too much, however, be forced upon an infant, it passes away in the stools. The peptone is taken up by the gastric veins as rapidly as formed, and being circulated through liver by the porta, may excite that organ to pour out bile for the next digestive step. The gastric juice is never free in the stomach in large quantity, but is being absorbed and re-secreted, which accounts in some degree for the stomach itself not being digested, but the rapid renewal of epithelium is also protective. The alkaline reaction of the circulating blood neutralizes also the acid of the gastric juice, according to Pavy, who, however, has shown that living frog's leg, if retained in the stomach of a dog, will be digested almost as rapidly as if dead. The stomach of man has, however, been found digested or softened, as described by Hunter, and the fact has medico-legal importance, as it may be mistaken for the effect of corrosive poisons or chronic ulcer. With regard to the action of the stomach on other substances, fat is only melted, sugar and gelatin probably absorbed, being the only calorific food the stomach acts on, while starch, cellulose, &c., are unaffected. Iron is converted into its oxide and peroxide.

Absorption from the stomach will be dwelt on in the next chapter; but it may be here stated that some substances are either not absorbed or are much changed in absorption. Thus, if emulsin be put in the stomach of a dog, and amygdalin in the veins, no formation of hydrocyanic acid or injury to the animal results; but, on the contrary, if the emulsin be introduced into veins and amygdalin into the stomach, rapid poisoning occurs. Gentle

exercise and mental quiet seem to promote digestion ; strong alcohol and metallic salts check it by throwing down the albuminoids. Bile has a most remarkable power in arresting the process, hence the connexion between misplaced bile and "indigestion." As we have seen, foods are not always of value according to the amount of nutritive matter they contain, but also according to their digestibility or rapidity of assimilation.

The time occupied by the digestion of an ordinary meal was said by Beaumont to range between 23 to 4 hours, fish and veal being the extremes. More accurate knowledge may be obtained by the plan invented by Blondlot of making fistula in animals, and disease has produced an admirable subject for experiment, as observed by Busch, who met with a case of jejunal fistula. His results are shown in the following table:

Appeared in Weight changed Proportion of
Minutes.

solids changed

from 1 to

from 1 to

Much fat, as in nuts, mushrooms, and many meats, is indigestible; and thus the flesh of wild animals, as venison, containing least of it, are most digestible. Some matters, as vegetable husks and skins, and yellow elastic tissue, pass quite unaltered, while bones are acted on, their salts being dissolved by the acid.

Besides rumination, or voluntary return of the food to the mouth, which characterizes a great class of animals, and has been seen in man, the food may leave the stomach by vomiting, or gases may be evacuated in vast quantity by eructation. The mucous surface seems to secrete gas in some cases, especially in old persons of weak digestion, or fermentation may evolve it, if it

Gases escape

occurs instead of mere digestive catalysis. most readily when the body is erect, as they rise to the cardiac orifice. Fresh powdered charcoal, which has great absorbent power for gases, I have found gives much relief in such cases.

The Act of Vomiting is accomplished by the stomach contracting while the cardiac orifice is open, the pyloric closed, so that it will not let fluid pass from the stomach, but will from duodenum, as seen in hernial vomiting. The abdominal muscles, also, press the stomach against the diaphragm, which is fixed and depressed by a previous inspiration. The glottis is closed during vomiting, so as to prevent expiration, and a loud, sudden inspiration often succeeds the act. Magendie believed the stomach was passive in vomiting, as he could produce it in a dog, whose stomach was removed and a pig's bladder substituted, by injecting tartar emetic into the veins. However, L'Epione saw the organ contract vigorously in a man whose abdominal walls had been accidentally ripped open, and the same has been demonstrated by vivisection on animals. The muscular action by which the contents of the stomach and intestines are forced in a reverse direction, as in strangulated hernia, is usually considered antiperistalic, or the opposite of the normal course. Dr. Brinton regards this explanation unnecessary, as, if there be an obstruction, the ordinary pressure will force the fluid back through the centre of the tube, as if one used a perforated piston. If, however, the œsophagus be removed from an animal into whose veins tartar emetic has been injected, the vermicular action is found to be towards the mouth. All excitants to vomiting act on the nervous centres or peripherythus, the sight or smell of a disgusting object, irritation of the medulla oblongata, mechanical irritants in the stomach, as mustard or salt, emetics absorbed or injected, and tickling the fauces, are either direct or reflex provocants of the act.