which regulate these varieties in the deposition from inflamed serous membranes. Under the influence of inflammation, also, whether acute or chronic, serous membranes are liable to form adhesions betwixt their opposite surfaces, and this may consist of simple adhesion with very little appearance of any interposed substance; or there may be an interposition of false membrane, which is often of very considerable thickness.

In their structure, serous membranes are liable chiefly to three morbid conditions.

1. Simple thickening. This is seen most strikingly in the peritoneum, which is sometimes found thickened in a most remarkable degree; and it appears to be the result of inflammation which has gone on in a chronic form.

2. Tubercular disease,-the whole surface of the membrane being found studded with innumerable tubercles, generally of a very small size, and of a firm consistence. They appear to be covered by cysts, and present the same characters with tubercles in other parts of the body.

3. There is another affection, often met with in the peritoneum, which appears to be in its nature quite distinct from tubercular disease. It consists in the surface of the membrane being covered by nodules of various shapes and sizes,-of a semi-pellucid character and smooth rounded surface. The masses of this substance are sometimes of great size, and a large extent of the peritoneum may be found covered by them. This is the disease described by Dr. Baron, and supposed by him to be of the nature of hydatids. On first inspection it has a resemblance to hydatids; but in the specimens which I have had an opportunity of examining, it appeared to be of an entirely different nature. The nodules were of a uniform firm gelatinous consistence, or even more dense at the centre than at the circumference. They did not appear to be covered by a cyst, and they were entirely soluble in boiling water.

II. The second structure is the Muscular Coat. It completely invests the whole extent of the canal; and the healthy function of the parts depends upon this muscular covering performing at all times its healthy and regular action. We know little of the diseases of muscular fibre, except in as far as relates to derangement of its functions. In a muscular covering which invests a cavity, the principal deviations from the healthy state appear to be the following.

1. A morbidly increased but uniform and harmonious action. This appears to arise chiefly from causes of irritation applied to the internal surface of such cavities. In this manner we see vomiting produced by various irritations applied to the stomach, and diarrhoea by similar causes applied to the intestinal surface. A similar effect seems to arise from a morbid irritability of the surface itself, provided it be uniform over a considerable extent of the membrane; the ordinary stimuli producing in this case the same effect that the irritating causes do in the healthy state of the membrane.

2. A morbidly increased but partial and irregular action. This appears to arise chiefly from morbid irritability of small portions of the internal surface; the ordinary stimuli producing, at these parts, a morbidly increased action, with which the other parts do not harmonize. This appears to be the state which is often expressed by the indefinite term spasm. It is seen in the urethra, and the œsophagus, in the affection which is called spasmodic stricture; and a similar condition appears to occur in the bowels, particularly in certain states of dysentery, in which we find frequent irritation and morbid discharges from the lower part of the canal, with retention of the natural feces in the parts above.

3. Diminution or loss of muscular power. In a muscular covering investing a cavity, this appears to arise from two causes, namely, over distention and inflammation. The former we see distinctly take place in the bladder, and

there is reason to believe that something similar occurs in the bowels in certain states of Ileus. Inflammation seems

also to destroy the action of muscular fibre. Thus, intestine which has been highly inflamed is generally found in a state of great distention, showing the complete loss of its healthy muscular action; and, if the disease has gone on until the intestine has either become ruptured, or has given way by ulceration, it is found to have fallen together like an empty bag, without any appearance of muscular contraction; whereas, healthy intestine, when it is empty, contracts uniformly into a round cord. In regard to the immediate effects of inflammation upon muscular fibre, there is considerable obscurity; but, one point may be considered as known and established, which is of considerable importance for our future inquiries, namely, that a result of inflammation in muscular fibre is gangrene. When, therefore, we find gangrene in the intestinal canal, we have reason in general to conclude that inflammation has existed in the muscular coat; for we shall afterwards find grounds for believing, that it may exist in each of the coats separately without affecting the others, but giving rise to most important diversities in the symptoms.

4. Thickening of the muscular coat has also been described by some of the French writers, particularly as occurring in the stomach. It constitutes an affection to which they have given the name of Hypertrophia of the stomach; though some of them appear to apply this term to a general thickening of all the coats.

III. The third structure to which our researches will refer, is the Mucous Membrane. This lines the whole course of the intestinal canal from the pharynx to the rectum. In the structure and functions of this membrane, we have to keep in view the following circumstances.

1. The whole surface of the membrane is constantly secreting a mucous fluid, which is transparent, glutinous,

and is said to have slightly acid properties. It appears to be formed in large quantity; according to Haller, to the extent of eight pounds in twenty-four hours. When an animal has fasted for a considerable time, this fluid has been supposed to undergo digestion, forming chyme and excrementitious matter; and, in this way, some have explained the appearance of excrementitious matter in tedious fevers, and other protracted diseases, in which the patient has taken little or no nourishment.

2. Besides this general secretion from the whole mucous surface, there is a distinct formation, from numerous follicles or simple glands, of a liquid which has been called the follicular fluid. These follicles exist in great numbers along the whole course of the intestinal membrane, though they are more numerous at some parts than at others. The peculiar properties of the follicular fluid have not been ascertained; but, it is considered as certain, that it is distinct from the general mucous secretion,-because, in observations upon living animals, the latter may be seen to be produced from portions of the membrane, where no follicles appear to exist. The mucous and follicular fluids of the stomach, mixed with similar fluids from the oesophagus, and with saliva, are considered as forming the gastric juice. 3. There is likewise from the whole mucous surface a serous exhalation, similar in its properties, as far as is known, to the exhalation from serous membranes.

4. The intestinal mucous membrane is also to be considered as an absorbing surface ;-numerous absorbents opening from every part of it, and conveying the absorbed fluids towards the thoracic duct. These are most numerous in the small intestines.

We are to attend to various forms of disease in mucous membranes connected with these peculiarities of structure. These are chiefly the following.

1. Inflammation and its consequences. This appears

to exist in mucous membranes in various forms, or rather various degrees, but we are ignorant of the causes which regulate these varieties. The effect of the first or lowest degree of inflammation on a mucous membrane, appears to be simply an increase of its proper secretion, more or less changed in its qualities from the healthy condition. This we see most familiarly in the nose and in the bronchial membrane. In another state of inflammation, we find the formation of aphthous crusts, and in a third the deposition of false membrane. This last we see most remarkably in the bronchial membrane; it is also met with, though more rarely, in the mucous membrane of the intestine. In a more advanced stage, inflammation of the mucous intestinal membrane terminates by ramollissement, or an ash-coloured pulpy degeneration of portions of the membrane; these fall out and leave spaces, which are apt to pass into ulceration. A considerable extent of the membrane is also occasionally found in a state of uniform dark softening, resembling gangrene. Adhesion of the opposite surfaces of the mucous membrane of the intestine is sometimes met with, producing complete obliteration of the canal; but this is very rare. A case has been related to me, in which it was found to have taken place in the parts included in a hernia. Inflammation of mucous membranes exists in a more chronic form, in which it goes on for a long period, and is chiefly distinguished by increased and morbid secretion from the parts. In its progress in these cases, the membrane is apt to become thickened and even indurated, so as considerably to diminish the capacity of the cavity. In this manner is formed stricture of the urethra, and similar diminution of the area of the intestinal canal. The diseased surface in those cases is frequently found covered with fungous elevations; and these frequently alternate with portions of the membrane in a state of ulceration. The French writers have started a contro