In all these instances, the fibrillated structure contains a certain amount of corpuscles, which lie in the meshes of its network. These have been termed " exudation-globules" by some authors,--by others " organic germs,"—and by others (especially Mr. Add ison) are regarded as identical with the white corpuscles of the blood. They may present considerable varie ties in size and appearance ; having in some instances the characters of fully-formed cells, whilst in others they rather resemble nuclei aggregations of granules. It seems difficult believe, that they can be identicalwith the wh. corpuscles of the blood ; since if the exudati has been poured forth by open orifices, su ciently large to admit these to pass, there WO be no obstacle to the escape of the red corp cles,—at least where the latter are of srna1 size, as in mammalia. They are probably be regarded as originating in the fibrinous posit, from germs which it contained, wh effused froin the vessels of which germs t white corpuscles may h'ave not improba been the parents. The degree of their de% lopement into cells would appear to depei upon the degree of plasticity of the depo Not unfrequently they seem arrested in th progress ; especially in cases where the exu tion verges towards a mco-plastic charact In the egg-membrane, very few of these c puscles are seen ; and as it is thus alm entirely composed of consolidated fibrin, possesses considerable toughness. The sa is the case with highly plastic exudations fr inflamed serous surfaces. But in depos. which are less plastic, we see a larger number these corpuscles, and a diminution and d creased tenacity of the fibres.; the membral then becomes quite friable, and approaches t character of a purulent exudation. The cac plastic deposits will be presently noticed, u der the head of Abnormal States of Nutritio At present we shall proceed to consider t application of these facts to the ordinary co ditions of that process.
The question naturally suggests its 'inane, whether any oE the tissues of the body arc formed by the simple effusion of h from the bloodvessels, and its subsequent con solidation in the manner already described. No such idea seems to have occurred to the continental physiologists, who, following in the path which had been marked out by Schwann, have sought to trace, for all the tissues, an imme diate origin in cells. But the writer does not find that any of them are sufficiently aware of the facts already detailed, in reg,ard to the definite structure which fibrin will assume, when it has undergone a high degree of elaboration, and has coagulated under the most favourable circum stances ; and with the greatest respect to their authority, he ventures to attach sufficient weight to the observations of Messrs. Gulliver and Addison, confirmed as they are by his own. to induce him to adopt a different explanation, which he offers with diffidence, to be confirmed or set aside by future enquiries.
The fibrous tissue existing in false mem branes, and still more that which has been dis covered by the writer in the egg-shell, may be reg,arded in his opinion as a type of those sim ple fibrous tissues, which form a larg,e porpor tion of the bulk of the body in the higher animals, and of which the function is purely mechanical. When we contrast the fabric of an animal with that of a plant, we are struck with this important difference in their conform ation,—that whilst the latter is made up solely of elements which are to perform their several parts in the performance of the nutritive and reproductive operations, (the only exception being in the case of those more solid portions of the fabric which are destined to give mechanical support to the remainder),—the former is composed of a much greater variety of parts, which are adapted to move upon each other. Now this purpose requires, not only the addition of certain new tissues, to vvhich nothing analogous is to be found in plants, for creating and exercising the motor power, but also an adaptation of the whole structure to this new condition. The tissues of plants entirely consist of cells, or simple modifications of them. Some of these cells being strengthened by in ternal deposits, form the solid woody fmme work of the stem and branches, which gives support to their wide-spreading foliage and numberless blossoms. Others coalesce, by the
disappearance of their intervening partitions, into tubes, which serve for the conveYance of fluid between the most distant parts. But the great bulk of the fabric still consists of cells, closely adherent to each other, and actively par ticipating in the various operations of organic life. In lihe manner in the animal body, a certain part of the cells have contributed to form the solid osseous and cartilaginous framework, which not only gives support and protection to the body, but contributes to its power of move ment, •by affording fixed points far the attach ' ment of its muscles. Others again have coal esced into vessels, as in plants, for the rapid !conveyance of fluids. Others, too, after a simi ,lar coalescence, have developed new, and re ',markable products in the interior of the tubes hus formed, and become transformed into those iervous and muscular tissues, to which nothing I analogous is found in plants, and which are the peculiar instruments of animal life. Yet still there remains a large number of unchanged cells scattered through the body, perform, as in plants, the essential part in the functions of nutrition, reproduction, &c. These, how ever, could not be held together in their con stantly-varying relative positions without some intervening substance altogether different from true cellular tissue. It must be capable of resisting tension with considerable firmness and elasticity ; it must admit free movement of the several parts upon one another ; and it must still hold them sufficiently close together to resist any injurious strain upon the delicate vessels, nerves, &c., which pass from one to another, as well as to prevent any perrnanent dis placement. Now all these offices are performed in a remarkably complete degree, by the areolar tissue,* the reason of whose restriction to the animal kingdom is thus evident. It is chiefly composed of interlacing fibres and shreds of membrane, which do not seem possessed of any other than simply physical properties; the small degree of vital contractility which it possesses in some spots (as in the dartos,) being attribut able to the intermixture of fibres analogous to those of the unstriated muscular tissue. One of itS most remarkable peculiarities is the ra pidity of its regeneration ; and this is obviously due, in part, to the large amount of bloodvessels by which it is traversed. The accounts given of its developement by Schwann and Henle do not by any means correspond ; and it appears to the writer, that the evidence of the partici pation of cells in the process, in any other way than as elaborating the fibrin, is very insuffi cient. The observation already quoted from Mr. Addison ( p. 746) seems to explain some appearances occasionally met with, which in duced those observers to assign a more direct cell-origin to this tissue; for he notices that the re mains of the white corpuscles, and little a,ggrega lions of the granules they had emitted, seemed to be the centres, as it were, of the fibrillation.t If vve once admit this doctrine in regard to areolar tissue, it is not difficult to extend it to those fibrous structures in general, which re semble it in the physical natme of their func tions ; and we shall then leave to the tissues of cell-origin, in animals as in plants, the perform ance of those operations which must be re garded as vital in their character. As an ad ditional argument in support of this view, the appearances presented by the semi-fibrous car tilages may be adduced. In the cartilages of the ribs, for instance, a more or less distinct fibrous appearance may be frequently seen in the intercellular substance ; this is sometimes so faint, that it might be considered as an illusion, occasioned by the manipulation to which the section has been subjected ; but it is often so well-defined, as almost to present the appear ance of the tnie fibrous structure. No indica tion of the direct operation of cells in the developement of these fibres has ever been wit nessed ; and we can scarcely do otherwise than regard them as produced by the regular ar rangement and consolidation of the particles of the blastema or plastic element, in virtue of its own inherent powers.