From this account of the extent and distribution of membrane, it will be found that it exceeds in quantity all the other solids of the body taken together, and enters as a principal ingredient into almost every portion of the animal frame. It serves indeed as a connecting medium between all the different organs by which they are held to gether, the basis to which they arc all attached, and the mould into which the particles of the other kinds of mat ter are deposited.
The mechanical structure of membrane is a subject which has exercised the ingenuity of many of the modern, anatomists, and has also formed a conspicuous feature in some of the most celebrated pathological hypotheses. In tracing the history of opinions, it will be necessary to take some notice of the theory that was formed on this subject by Boerhaave ; which, although in itself highly improbable, and scarcely supported by a single fact, or by any fair analogy, was at one period very generally em braced, and was even adopted, as the basis of much patho logical and physiological reasoning. He conceived that there was a kind of hypothetical fibre, almost infinitely minute. and th.it by the union of these fibres, a membrane is composed of the first order ; and that this, when coiled up, forms a vessel of the first order. These vessels, by being placed in contact, form a membrane of the second order, and these again arc coiled up into a vessel of the second order ; and, by the repetition of this process, we obtain vessels and membranes of any assignable magni tude. It follows, as the direct consequence of this hypo thesis, that, except the earth of the bones, no part of the body is properly solid, besides the coats of the vessels, and that all the parts which appear to be solid, are in fact nothing more than a congeries of vessels, arranged in these regularly ascending series. Although this i.oct•ine was directly in contradiction, both to the results of anato mical injections, and of observations made by the mi croscope, and, in fact, may be considered as resting solely upon the credit of its inventor, yet so powerful was the authority of Boerhaave, in every point connected with medical science, that•it acquired all the force of Haller's reasoning, as well as that of his most acute contempora ries, to controvert the doctrine.
The opinion which Haller endeavoured to substitute for that of Boerhaave was, that the membranous matter is composed of a vast assemblage of infinitely minute lines or fibres, connected together by either lines or plates, ac cording to the structure of the parts to which they belong; Ile was at much pains to exhibit this fibrous structure in all parts of the body, and to trace their connexion with each other, by means of what he calls the cellular web, which he conceived to form the mechanical basis that unites all the various parts into one whole.
This doctrine of Haller is no doubt much more correct than that of his preceptor, but still it must be regarded as, in sonic measure, hypothetical, and as partaking of that metaphysical spirit, which is not yet entirely banished front our physiological reasoning. He speaks of the ori ginal or fundamental fibre as being inorganic, and seems to consider it necessary that we should possess a certain number of these inorganic fibres, before we arrive at one which is entitled to be considered as properly organized matter. He also supposed that, in the formation of the larger parts from these ultimate fibres, there arc inter vening spaces, which are filled up with an inorganic con cretion, a doctrine which we apprehend to be quite in consistent with any correct conception of the nature of the living body. The fibre itself may he conceived not to be vascular, but still we must suppose that there is no part which is not within the action of some of the vital organs, and is not therefore properly alive; although with respect to the degree, and even the nature of their vi tality, the different parts may be essentially different.
With respect to the actual appearance which the mem branous matter presents to the eye, when assisted by the microscope, we learn from the observations of Fontana, that it consists of a number of flattened plates, which he calls primitive fascia, and which are connected together by a cchular web of a more lax texture. These fasci?, when macerated, or divided as much as possible by me chanical means, are found to be made up of cylinders in the form of solid threads, of a spiral or waved form, which are neither hollow nor vascular, and which appear to be of the same kind in all parts of the body. These tendi nous threads are said to be about the 13,000th of an inch in diameter. Ample experience has proved, that all mi croscopical observations are to be received with great caution ; but the account of Fontana is given with so much candour, and appears in itself so reasonable, that we are disposed to place some confidence in it.