Bichat's mode of examining histology had been preceded immediately by the discoveries of Haller. Haller attributed a special force, irritability, to those of the animal fibres which contract by the effect of contact with external bodies: the greater the irritability, the greater the contraction. He denominated sensible fibres, those which, on being touched, transmit an impression to the mind.* He and almost all the physiologists of his epoch studied especially the parts and tissues of the body with reference to their sensible and irritable nature. But he thence deduced that to the organized living fibres belong certain determinate forces, which are called into action by the most diversified external influences, by the aid of which the organic fibres are distinguished as well from all inorganic bodies, as among themselves. It was easy to conceive the idea of a physiological force of the tissues, and to discover that particular physiolo gical operations are the result of special animal substances, irritable, and reacting in a manner peculiar to each one. The reflections of Pinel upon the analogy of pathological phenomena in the membranes of the different organs exerted considerable influence upon Bichat, as he himself acknowledges. "Of what consequence is it," said this great physician, "that the arachnoid, the pleura, the peritoneum, are situated in different parts of the body, since these membranes have a general conformity in their structure? Do they not undergo analogous lesions in a state of inflammation, and must they not be reunited in the same order, forming only different species ?" It was an idea as bold as it was fruitful to compare diseases of the mucous membrane of the stomach with catarrh of the pituitary membrane and blennorrhagia. Pinel established thereby the first basis of the natural classification of diseases according to their anatomical characteristics, a classification of which our epoch is so proud; but he rendered double service to histology by interesting physicians in its progress, and by teaching them to avail themselves, for the distinction of the tissues, of the manner in which they were affected in a morbid state. Finally, we must not omit to mention the part which the advancement of the physical sciences already so marked took in the labors of Bichat. He himself observes, in order to find fault with it, how much the method pursued by the physiologists differs from that adopted by philosophers: the philosopher sees every where phenomena of weight, elasticity, &c.; the chemist ascribes all those which he witnesses to affinity; but the physiologists had not yet ascended from the phenomena to the properties of matter which produce them. Consequently the first thing to be done in physiology is to investigate the properties, organic and vital, of animal substances. The different tissues are then, according to Bichat, so many different substances, endowed with particular forces, by the concurrence of which the organs are formed, and with properties upon which depends the action of these organs, almost in the same manner as the motion of a machine is the consequence of the elasticity of metal and the weight of water. He describes each tissue according to its chemical and physical characteristics, its vital properties and its morbid changes. The materials necessary to fill up this outline were supplied to him almost entirely by his own researches, by vivisections, by dissections, by separating the tissues by the aid of the knife, by maceration, and by chemical re-agents. In France where Bichat propagated his doctrines himself by public teaching, and where his death, the consequence of every species of excess,‡ caused general emotion, his opinions soon took deep root. They were known in Germany Mémoire sur la nature sensible et irritable des parties du corps animal. Lausanne, 1756, t. 1, p. 7. + Nosographie philosophique, 6th edition, Paris, 1818, introduction, p. xvii. The first edition appeared in 1798. I am told that this is not true, and that Bichat led a most exemplary life. Be that as it may, the expression used, "suite d'excès de tous genres," is susceptible of no other meaning. (M.)-Trans. by the translation of the General Anatomy, published by Pfaff; but they did not begin really to flourish there until Walther had animated them somewhat with the spirit of philosophy which prevailed at that time in the countries beyond the Rhine. Nevertheless the system of Bichat fell short of the end which the author had so clearly in view, and which he made such efforts to attain. The tissues which he considers as simple, and which in their quality of elements of organic bodies he compares to hydrogen, carbon, nitrogen, &c., are the following: 1. The cellular tissue. 2. The nervous tissue of animal life. 5. The tissue of the veins. 6. The tissue of the exhalant vessels. 7. The tissue of the inhalant véssels and of their glands. 8. The osseous tissue. 9. The medullary tissue. 10. The cartilaginous tissue. 12. The fibro-cartilaginous tissue. 13. The muscular tissue of animal life. 15. The tissue of the mucous membranes. 17. The tissue of the synovial membranes. 18. The glandular tissue. Among these tissues there are very few which are simple and homogeneous. The greater part of them are organs, some composed, as the arteries, the veins, the lymphathics, the serous and mucous membranes, of many tunics of a different structure and endowed with different vital properties; others resulting from particular elements combined with the cellular tissue and the vessels. Some organs of a formation evidently specific, are omitted, such as the yellow ligaments, the crystaline lens, and the cornea. Some tissues of a similar nature are found subdivided into two or three classes. Many of these errors were speedily discovered, and the histologists who succeeded Bichat suppressed certain tissues, for instance that of the exhalant vessels, united others under a common appelation, and added some new ones, as the erectile system of Richerand, and the elastic tissue of Cloquet. The attempt was also made to group the tissues; for example, by dividing them into general and simple (Meckel,) or into simple and compound (Rudolphi, R. Wagner,) or into simple, complex, and compound (E. H. Weber.) All these systems were modifications of that of Bichat; but their authors abandoned little by little the principle which had served as a starting point for the founder of the system; and although many of them arranged the materials in a more convenient order, nevertheless it was impossible with the insufficient means employed, to arrive at a vigorous classification. It is neither the external appearance nor chemical action of the tissues which can furnish the essential characteristics by which to distinguish them from each other. Their physiological functions are important, no doubt; but the functions of many of the tissues are uncertain, and it has happened much more frequently that the identity of function has been admitted on account of the analogy of structure with other known tissues, than that the morphologic identity of two tissues deduced from a real knowledge of their functions. Thus, for instance, the contractility of the middle tunic of the arteries was denied, because great weight was attached to a superficial resemblance between this tunic and the elastic tissue, whereas à more profound investigation of its physiological resemblance would have led to a comparison between it and the muscles of organic life. An acquaintance with the structure of the tissues, properly speaking, upon which must be based every good classification, is impossible without magnifying them greatly; for certain organs appear homogeneous to the naked eye, which are really composed either of fibres or of granulations, or of both, while other organs which are formed of elements totally different, resemble each other in their purely physical qualities. The following investigations will furnish abundant proof in support of this assertion. In fact, the microscope had already been in use for a long series of years; but it was confined to the hands of a small number of persons, who pursued a separate course. It was at first the simple pleasure of seeing wonders concealed from the naked eye, that induced Leeuwenhoek, Ledermuller and Gleichen to make observations. He first mentions frequently, in his letters, how the idea occurred to him one beautiful morning, to examine such and such substances, to-day the tartar on his teeth, to-morrow the deposit in his wine. This first period of infantile curiosity all those passed through in their turn, into whose possession a microscope fell. Leeuwenhoek was also frequently led by one discovery to a series of methodical observations, and often he made the happiest applications of his instrument to the physiological functions, for example, to the circulation of the blood, and to generation; but he never thought of comparing together the elements of the different organs. It is only in pursuance of his own good pleasure that he describes the fibres sometimes as tendons, sometimes as muscles or vessels, and the cellules as granulations, vesicles or scales. Toward the close of the preceding century excellent microscopic observations of some liquids had been made in England, in Holland, and in Italy; we may mention particularly in this connection Hewson, Muys, and Fontana; but it was not until 1816 that Treviranus undertook to resolve the tissues into their simple elements, easily discovered by the aid of the microscope, that is to say, into parts of a legitimate form, by reference to which we see clearly that they are not accidental fragments, and of which each one possesses the properties of the whole. These were called the elementary parts. Treviranus and most of the contemporary observers admitted three kinds of elements: 1st, homogeneous or amorphous matter; 2nd, cylinders or fibres; 3rd, globules. In place of the tissues of Bichat's system, figured here and there at that time the elementary parts. We find sometimes in the works of histologists the expression, "the muscular tissue," "the osseous tissue," "the vascular tissue," &c., replaced by those of "the muscular fibre," "the osseous fibre," "the vascular fibre." But this was the period in which men preferred to build up systems rather than to search for facts, and in which they selected from among the actual observations, not the most certain, but those which were best adapted to their own views. Was a general anatomy possible while the most erroneous ideas prevailed with regard to the intimate structure of the most extensive of all the tissues, of that which entered into the composition of almost all the parts, the cellular tissue, which the majority considered as an amorphous mucus, indeterminate, but susceptible of the most diversified developments? It was necessary to begin with the study of this tissue, and since it was described almost simultaneously (1834,) and nearly in the same manner, by Krause, Lauth and Jordan, we see discoveries succeeding each other with such rapidity, that the zeal for making observations does not leave time now for the establishment of a system. May this state of things continue for a few years longer! We have many materials to collect before it will be necessary, before it will be even prudent, to arrange and to classify them. The only thing is not to lose sight of the end in view, and to advance continually, sustained by the hope of attaining it. In fact, it becomes more and more manifest every day, that the same tissues regulate the same functions in all the organs, that the different physiological phenomena depend upon elementary parts morphologically and chemically different, and that a time will come when we shall be able, as Bichat desired, to reduce organism to a certain number of simple tissues, the names of which will recall the idea of determinate vital actions, in the same manner as an inorganic body is connected inseparably with the idea of specific gravity, of friability, of elasticity, &c. But microscopic studies have produced other fruits still. The human mind has always been disposed to bring back the different forms of creation to a small number of simple primitive parts. It is to this innate tendency that the systems of Epicurus and of Leibnitz owe their origin, both of whom conceived their atoms, their monads, without reference to observation and without the slightest hope that it would ever confirm their views. Urged knowingly, or unwittingly, by the same instinct, many moderns have endeavored, arming themselves with the microscope, to reduce the body into particles of similar form. The first which were observed before people had learned to distrust the instrument, were optical illusions, undulatory filaments and globules, which under certain circumstances are to be seen in every transparent object. Oken considered the infusory and spermatic animalcules as real monads. According to him the superior organisms, animal and vegetable, are composed of smaller animated beings, which have renounced their independent existence for a certain period of time. Dællinger and his school constructed the body of globules of blood, put in motion in the unwalled fissures of matter, susceptible of being united with the latter, to be afterwards separated from it, and to which C. Mayer even went so far as to attribute a particular lite, sensibility and spontaneous motion. Heusinger explained in the following manner how the fibres and tubes may proceed from spherical elementary particles: the sphere is the expression of an equal contest between contraction and expansion; it is on that account that all the organisms, all the organic parts, were originally globules; when the forces experience a greater tension, the vesicle is seen to emanate from the globule, which has often only the appearance of homogeneity; when the globules and the amorphous mass meet in organism, they are arranged into series, according to the laws of chemistry (?), and form fibres; when the vesicles are placed one after another we have canals and vessels. We see that this theory singularly approximates the truth, although the facts alledged in support of it are some of them inaccurate, and others badly explained; for Heusinger classes, for instance, among the simple vesicles, not only the adipous and mucous follicles, but also the serous membranes, and he considers the valves of the lymphatics as traces of the previous separation of the vesicles which have united to form these vessels. What Raspail says of the formation of molecules or organic atoms, of their configuration and of the forces by which they are animated, rests already upon a better foundation. At the moment of its formation, the organic molecule, reduced still to its most simple chemical expression, results from a combination of hydrogen and carbon; it is liquid and oleaginous, and enjoys already the faculty of aspiration; placed in atmospheric air, it absorbs principally oxygen, and like all liquid molecules, it assumes the spherical form as soon as it is suspended in water. At the same time that it absorbs atmospheric gases, it has a tendency to combine with inorganic bases. When this combination has once become intimate, the sphere is composed: 1st, of a vesicular envelope permeable to certain gases and to certain liquids, capable of developing itself and of enlarging; 2nd, of a liquid which continues to be organized within this envelope. The vesicle is then an organ endowed with the faculty of reproducing itself ad infinitum, and organizing according to its type the liquid which fills it and animates it. Whenever we have under our eyes the wall of a simple cell, in its fresh state, it is impossible, however much it may be magnified, to discover in it the least structure, that is to say that it seems to be homogeneous; but analogy leads us to believe that this membrane so simple in appearance, is composed of primitive globules, ranged spirally around the ideal axis of the cell. It must be admitted then, necessarily, that the wall of the maternal cell results from globules of the same nature and of the same apti tude for development, so that we can conceive of a cell formed, and so to speak, paved with globules all touching each other at six points of their equator, and whose axis is confounded with the radius of the sphere of which their union delineates the envelope. These globules are all equal, all endowed with an equal aptitude for development; but those only are developed, which meet at the points of intersection of two spires moving in a direction opposite to each other. Raspail compares these cells to crystals, atoms of organic creation, and gives to organization the name of crystalization in vesicles, vesicular crystalization. The organic cell is a crystal which absorbs gases and liquids, in order to convert them into internal organs; it is enlarged by organs of the same nature and the same aptitude engendered within itself, while the inorganic crystal increases only in surface, by the aid of successive juxta positions, and end to end. As soon as the chemical elements are united in the form of cells, they acquire particular forces, and constitute a separate kingdom, the organic kingdom. Give me a vesicle capable of absorbing, exclaims this author, parodying Archimedes, "and I will make you an organism." Raspail refers, in support of his theory, to the cells of starch in the vege table kingdom, and to those of fat in the animal kingdom. He examined profoundly those tissues which are really most likely to give rise to the idea that vegetables and animals resemble each other in their elementary parts. As it had already been demonstrated, with respect to the tubulous and fibrous tissues of vegetables, that they are produced by cells extended or confounded together, Raspail adopted these views for the animal fibres also. Dutrochet arrived at the same results by a comparison of the intimate structure of the animal, with that of the vegetable tissues. He discovered that the elements of the salivary glands, and the gray substance of the brain are utricles, of which those of the cerebral matter present, upon their walls, a multitude of opaque punctuations, exceedingly small, which he compared, improperly, to the numerous punctuations of the vegetable cells. He concluded, moreover, that the globules which compose, by their agglomeration, the greater part of the animal organs, are small membranous vesicles containing a liquid. This consideration induced him to reject the former distinction established between the solids and the liquids of the body: the solids are aggregates of globules having a certain solidity; the liquids, such as the blood, are equally aggregates of globules, but disconnected; and in animals there are certain component parts in which the globules are so slightly connected, that we do not know whether we ought to consider them as liquids, or as solids. There is but a single organic solid, the membrane of the urticle, or of the cell; the contents of this latter may very well become solid too, but life exists, at least with a certain degree of activity, only so long as the substances contained in the cells are liquid; the solid contents of the cells that have grown old have generally become strangers to life. The muscular fibres, and the other animal fibres, are only cells very much elongated, as we find them among the vegetables. Nature follows then a uniform plan in the intimate structure of all organized substances, as well animal as vegetable. The one and the other agglomerations of utricles, sometimes globular, sometimes elongated. The elementary utricles, as Dutrochet calls them, all have a general resemblance, and differ only in the nature of the liquids they contain. Nevertheless, the difference in the liquids they contain establishes a difference in the intimate nature of the membrane which forms the elementary utricle, for it is this membrane which secretes the liquid contained in the interior of the cavity which it forms. Neither Raspail nor Dutrochet has attempted to establish the laws of the organic development which they have announced with so much boldness, and, it must be confessed, with such beautiful simplicity, for the different animal tissues. Their observations are deficient in this respect; their theory has therefore remained stricken with sterility, and has passed unnoticed. Besides, neither the one nor the other observed, or at least has mentioned, an organ which plays a very important part in the development of the cells; I mean the nucleus. |