strated that the globules of the beings of the two kingdoms are alike in size, it would by no means follow that they should be identical in intimate composition. The discordance, which we have deplored, is strikingly applicable to the case before us. The appearance of the memoir of Dr. Edwards excited the attention of M. Dutrochet, and in the following year his "Recherches" on the subject were published, in which he asserts, that the globules, which compose the different structures of invertebrated animals, are considerably larger than those of the vertebrated; that the former appear to consist of cells, containing other globules still smaller; and hence he infers, that the globules of vertebrated animals are likewise cellular, and contain series of still smaller globules. Dr. Edwards, in his experiments, found, that the globules of the nervous tissue, whether examined in the brain, in the spinal cord, ganglia, or nerves, have the same shape and diameter, and that no difference in them can be distinguished from whatever animal the tissue is taken. M. Dutrochet, on the other hand, considers, with Sir Everard Home, and the brothers Wenzel, that the globules of the brain are cellules of extreme minuteness, containing a medullary or nervous substance, which is capable of becoming concrete by the action of heat and acids. This structure, he remarks, is strikingly evidenced in certain molluscous animals; and he instances the small pulpy nucleus, which forms the cerebral hemisphere of limax rufus, and helix pomatia, and is composed of globular, agglomerated cellules, on the parietes of which a considerable number of globular or ovoid corpuscles are perceptible. (Fig. 310.) Fig. 310. (Dutrochet.) M. Dutrochet, again, did not find the structure of the Cellules of Brain. nerves to correspond with that of the brain. He asserts, that the elementary fibres, which enter into their composition, do not consist simply of rows of globules, according to the opinion of M. Edwards and others, but that they are cylinders of a diaphanous substance, the surface of which is studded with globular corpuscles; and that, as these cover the whole surface of the cylinder, we are led to believe that they are in the interior also. After detailing this difference of structure between the brain and the nerves, the former consisting chiefly of nervous corpuscles, the latter chiefly of cylinders or fibres, M. Dutrochet announces the hypothesis, which exhibits too many indications of having been formed prior to his microscopic investigations,-that these cerebral corpuscles are destined for the production of the nervous power, and that the nervous fibres are tubes, filled with a peculiar fluid, by the agency of which nervimotion is effected. For further developements of the views of M. Dutrochet, the reader is referred to the work itself, which exhibits all the author's ingenuity and enthusiasm, but can scarcely be considered historical. The beautiful superstructure of M. Edwards, and the ingenuity of M. Dutrochet, were, however, most fatally assailed by subsequent experiments of Dr. Hodgkin with a microscope of unusual power. The globular structure of the animal tissues, so often asserted, and apparently so clearly and satisfactorily established by M. Edwards, is, as we are told by Dr. Hodgkin,' a mere deception; and the most minute parts of the areolar membrane, muscles, and nerves, were again referred to the striated or fibrous arrangement. A part of the discrepancy between MM. Edwards and Dutrochet may be explained by the fact of the former using an instrument of greater magnifying power than the latter, who employed the simple microscope only; and it was observed, that when the former used an ordinary lens, the arrangement of a tissue appeared cylindrical, which, with the compound microscope, was distinctly globular. The discordance between Messrs. Edwards and Hodgkin was reconcilable with more difficulty. On the whole subject, indeed, minds were kept in a state of doubt, and the rational physiologist waited for ulterior developements. MM. Prévost and Dumas, and M. Edwards, farther affirmed, that all the proximate principles-albumen, fibrin, gelatin, &c.,-assume a globular form, whenever they change from the fluid to the solid state, whatever may be the cause producing such conversion. M. Raspail-a wayward genius, who has quitted the sober pursuit of science, for the uncertainty and turmoil of politics, from which he has suffered greatly-ranged himself among those who considered, that the ultimate structure of all organic textures is vesicular, and that the organic molecule, in its simplest form, is an imperforate vesicle, endowed with the faculty of inspiring gaseous and liquid substances, and of expiring again such of their elements as it cannot assimilate; properties, which he conceived it to possess under the influence of vitality. His views contain, perhaps, the germ of those that follow, and that now occupy the minds of observers. Fig. 311. The microscopical researches of Schwann and Schleiden3 led them to affirm, that the new-forming tissues of vegetables originate from a liquid gum or vegetable mucus, and those of animals probably from the liquor sanguinis-which consists essentially of fibrin-after transudation from the capillary vessels. This matrix, in a state fully prepared for the formation of the tissue, is termed by them intercellular substance and cytoblastema. In the first instance, it exhibits minute granular points, which grow and become more regular and defined from the ag glomeration of minuter granules around the larger, constituting nuclei or cytoblasts or cell-germs, and having, when fully formed, and in fact formed before them, one or more well-defined bodies within, called nucleoli. From the cytoblasts, cells-primordial or germinal cells are formed. A transparent vesicle grows over each, and becomes filled with fluid; this gradually extends and becomes so large that the cytoblast appears like a small body within its walls, and hence the cell is said to be nucleated. The form of the cells is at first irregular, then more regular, and they are alternately flattened Primary Organic Cell 1 Op. citat., p. 466. 2 Op. citat., § 126. 3 Mikroskopische Untersuchungen über die Uebereinstimmung in der Struktur und dem Wachstum der Thiere und Pflanzen, von Dr. Th. Schwann und Schleiden, in Müller's Archiv., p. 137, 1838; and Microscopical Researches into the Accordance and Growth of Animals and Plants, translated by Henry Smith, Sydenham Society edition, London, 1847. Fig. 312. оо Plan representing the formation of a Nucleus, and of a Cell on the Nucleus, according to Schleiden's view. by pressure against each other, so as to assume different forms in different tissues. Such is their description of the vegetable cells from which all the tissues. of plants take their origin. In like manner, the tissues of animals are formed from a fluid, in which nucleoli, nuclei or cytoblasts and cells, are successively developed. The globules of lymph, pus, and mucus, are cells with their walls distinct and isolated from each other; horny tissues are cells with distinct walls, but united into coherent tissues; bone, cartilage, &c., are formed of cells whose walls have coalesced; areolar tissue, tendon, &c., are cells which have split into fibres, and muscles, nerves, and capillary vessels are cells whose walls and cavities have coalesced. These cells seem to possess an independent and limited life, which has no immediate connexion with that of the organism; the decomposition constantly taking place in the living body being connected with the death of the cells of which the several parts are constructed; and for the reintroduction of which into the circulating fluid, the lymphatic system appears to be specially destined. By virtue of this vital power, they not only attract but change the substances brought in contact with them, or have a power of self-nutrition; and that this is probably independent of the nervous system is shown by an experiment of Dr. Sharpey, in which the reproduc tion of a portion of the tail of a salamander took place, although it was cut off, after the organ had been completely paralysed by dissecting out at its root a portion of the spinal cord, together with the arches of the vertebræ. To the doctrine of cell formation, Professor Goodsir,' of Edinburgh, has, of late years, made several important additions. Amongst other observations, he states, that besides all organs and tissues having their origin in and consisting essentially of simple or developed cells possessed of a special independent vitality, the component cells are divided into numerous departments, each of which consists of Fig. 313. ritous Tumour. several cells arranged round one Endogenous Cell-growth in Cells of a Melicecentral or capital cell, which latter is the source whence all the other cells in its own department de a. Cells presenting nuclei in various stages of developement into a new generation. b. Parent-cell filled with a new generation of young cells, which have originated from the granules of the nucleus. 1 Anatomical and Pathological Observations, p. 1, Edinb., 1845. rived their origin. To each of these several central nucleated cells he gives the name nutritive centre or germinal spot. Each nutritive centre possesses the power of absorbing materials of nourishment from the surrounding vessels, and of generating, by means of its nucleus, successive broods of young endogenous cells, which from time to time fill the cavity of the parent cell, and, carrying with them its cell-wall, pass off in certain directions, and under various forms, according to the texture or organ of which the parent forms a part. There are two kinds of nutritive centres,-those peculiar to the textures, and those belonging to organs. The former are in general permanent; the latter peculiar mostly to the embryonic state, and ultimately disappearing; but there is one form in which the nutritive centres are arranged both in healthy and morbid parts, which constitutes what Mr. Goodsir calls a germinal membrane. It is only met with on the free surface of organs or parts. It is a fine transparent membrane, consisting of cells arranged at equal and variable distances within it. The centres of these component cells are flattened, so that their walls form the membrane by cohering at their edges, and their nuclei remain in its substance as germinal centres. One surface of the membrane is attached to that of the organ or part, and is, therefore, applied upon a more or less richly vascular tissue; the other is free, and it is to it only that the developed or secondary cells of its germinal spots are attached. These secondary cells, whilst forming, are contained between the two layers of the germinal membrane; but as they become developed, they carry forward the anterior layer, and become attached to the free surface, whilst the nuclei are left in the substance of the posterior layer in close contact with the blood vessels, from which they derive the materials for the formation of new cells. The doctrine of the developement of all the organic tissues from cells is now embraced by almost all histological inquirers; yet there are some who doubt it; and others, who by no means regard it as applicable to all the tissues. Thus M. Mandl' objects to the term cytoblastema as applicable to the matrix or organizing material of the tissues, because it necessarily involves the supposition that it gives origin to cells. According to him, the elements, that are developed in the blastema as he prefers to call it-do not generally deserve the name of cells, inasmuch as they may either liquefy as in the glands; consolidate as in the amorphous membranes; or become transformed directly into fibres, as in the areolar tissue. Mr. Gulliver, too, has inferred from his observations, that the mere extension of the parietes of cells is not essential to the formation of all tissues, since fine fibres or fibrils are found in fibrin that has coagulated even out of the body. He has given several figures to exhibit the analogy of structure between false membranes and fibrin coagulated after death, or after the removal of the blood from the body. Schwann, on the other hand, lays down the rule, which he considers of universal application, that all organic tissues, however different they may be, have one common principle of 1 Manuel d'Anatomie Générale, p. 549, Paris, 1843. 2 Appendix to Gerber's Anatomy, Atlas, p. 60, and Figs. 244–6, Lond., 1842. 2 developement as their basis, the formation of cells; that is to say, nature never unites molecules immediately into a fibre, tube, &c.; but, always, in the first instance, forms a round cell; or changes, when it is requisite, the cells into the various primary tissues, as they present themselves in the adult state; but "how," says Mr. Gulliver, "is the origin of the fibrils, which I have depicted in so many varieties of fibrin, to be reconciled with this doctrine? and what is the proof that these fibrils may not be the primordial fibres of animal textures? I could never see any satisfactory evidence, that the fibrils of fibrin are changed cells; and indeed, in many cases, the fibrils are formed so quickly after coagulation, that their production, according to the views of the eminent physiologist just quoted [Schwann], would hardly seem possible. Nor have I been able to see, that these fibrils arise from the interior of the blood-disks, like certain fibres delineated in the last interesting researches of Dr. Barry." Mr. T. Wharton Jones, also, has considered the notion entertained by Dr. Barry,3 that a fibre exists in the interior of the blood corpuscles, and that these fibres, after their escape from them, constitute the fibres which are formed by the consolidation of the fibrin of the liquor sanguinis, to be erroneous. He regards the appearance as altogether illusive. Dr. Carpenter, in remarking on Mr. Gulliver's figures, all of which, as he properly observes, clearly show, that a small portion of coagulated fibrin contains a far larger number of fibres than we can imagine to be contained in the number of blood-disks that would fill the same space, states, that he has discovered a very interesting example of a membrane composed almost entirely of matted fibres, which so strongly resembles the delineations of fibrous coagula given by Mr. Gulliver, that he cannot but believe in the identity of the process by which they are produced. This is the membrane enclosing the white of the egg, and forming the animal basis of the shell. If the shell be treated with dilute acid, a tough membrane remains, exactly resembling that which lines it; and if the hen has not been supplied with lime, there is no difference between the two membranes even without the action of acid on the outer one. Each of them consists of numerous laminæ of most beautifully matted fibres intermixed with round bodies exactly resembling exudation cells. It is in the interstices of these fibres, that the calcareous particles are deposited, which give density to the shell. These membranes, according to Dr. Carpenter, are formed around the albumen, which is deposited on the surface of the ovary during its passage along the oviduct, from the interior of which the fibrinous exudation must take place. It is clear, then, that this doctrine of the origin of all the tissues from cells cannot be considered established. We believe, indeed, with a recent writer,' that most physiologists, who are not prejudiced by the seductive simplicity of Schwann's generalization as to the derivation of 1 Lond. and Edinburgh Philosoph. Magazine, Oct., 1842. 2 Proceedings of the Royal Society, No. 56. 3 Philosophical Transactions for 1842. Origin and Functions of Cells, in Brit. and For. Med. Rev. for Jan., 1843, p. 277. 5 Brit. and For. Med. Review, July, 1844, p. 95. |