GENERAL ANATOMY.
SYSTEMS
COMMON TO ALL THE APPARATUS.
GENERAL OBSERVATIONS.
The organized systems of the living economy may be divided into two great classes. One, generally distributed and every where present, concurs not only in the formation of all the apparatus, but even in that of the other systems, and offers to every organized part a common and uniform base; this includes the cellular, arterial, venous, exhalant, absorbent, and nervous systems. The other, on the contrary, placed in certain determinate apparatus, foreign to the rest of the economy, has a less general and oftentimes an almost insulated existence; this embraces the osseous, cartilaginous, fibrous, muscular, mucous, serous systems, &c. &c.
The first part of this work will be devoted to the examination of the general systems, of the generative systems, if I may so express myself, systems which are not however of such importance that all the organized parts are necessarily provided with these six. In fine, in some there are neither arteries nor veins; in others nerves; in some but little cellular texture; but they concur to form the greatest number, and some are always found where others are wanting. Thus in the tendons, in the cartilages, &c. which are deprived of blood, there are exhalants, absorbents, &c.
In general, it appears that the exhalant and absorbent systems are the most universally diffused. Nutrition supposes this; in fact this function is the result of a double movement; one of composition, which brings to the organs, the other of decomposition, that carries from them the nutritive matter; now the exhalants are the agents of the first movement, and the absorbents of the second. As every organ is nourished, and as the mechanism of nutrition is uniform, it follows that these two systems belong to all the organs. After them the cellular system is the most generally found. Where there are no blood vessels, it is sometimes met with, and it always exists where these vessels are. Next to this, the arteries and veins are spread to the greatest number of parts. Oftentimes no nerve is discoverable, where they penetrate, as in the aponeuroses, the fibrous membranes, &c. &c. The nervous is of all the generative systems, that which is found by dissection in the smallest number of parts. The serous membranes, the whole fibrous system, the cartilaginous, the fibro-cartilaginous, the osseous, &c. appear to be deprived of it.
Particularly destined to form a part of the structure of other organs, the generative systems perform the same office for one another; thus the cellular texture enters into the composition of the nerves, and the arteries and veins; and the arteries and veins are ramified in the cellular texture, &c. It is a general intermixture of one with the other.
It may be imagined, from what has now been said, that the generative systems, considered under the relation of organs, forming a common and uniform base for all, ought to be sooner developed than others; and this, observation proves. While there is hardly an outline of the others in the first months of the fœtus, these predominate in a remarkable manner. The nerves, and their centre, which is the brain, the arteries, the veins and their central organ, which is the heart, the cellular texture, the exhalants and the absorbents, exhibit this phenomenon in a striking degree. Mere inspection suffices to prove this in the nervous, arterial, venous and cellular systems; in the other two it is proved by the wonderful activity of absorption and exhalation, at this period of life.
From what has just been said of the general systems of the economy, it is easy to perceive that they perform the most important part of nutrition. They form the nutritive parenchyma of each organ; now I call the nutritive parenchyma, the cellular, vascular and nervous outline of that organ. It is in this outline that the nutritive matter is deposited. This matter being different for each organ, establishes a difference between them. For the bones, it is phosphate of lime and gelatine; it is gelatine alone for the cartilages, tendons, &c.; fibrin for the muscles, albumen for certain other organs; so that if the nutritive parenchyma of a bone was filled with fibrin, it would be a muscle in the form of a bone, and vice versa, a muscle would become a bone with a muscular form, if its parenchyma was filled up with earthy and gelatinous substances. We should know the nature of all the living parts, if their nutritive substances were known to us; but the most of them are unknown, it is chemistry that must enlighten us upon this subject. All the organs resemble each other in their parenchyma, or at least have a great analogy. If it were possible to remove, from all the nutritive matter and leave this parenchyma untouched, we should see only among them, varieties of form, of size, of deposition of cellular layers, of vascular or nervous branches, but not of nature and composition.
In the first period after conception, the mucous mass that represents the fœtus, appears to be only a compound of the general systems. Each organ has as yet only its nutritive parenchyma, the parenchyma upon which nature has imprinted the form of the organ, that is to be developed there. In proportion as this outline is increased, the nutritive substances penetrate it, and then each organ, which until that time had been like the rest in its nature, and forming with them a homogeneous mass, begins to be distinct, and have a separate existence; each one draws from the blood the substance that is proper for it. This addition gives the attributes of thickness, of density, and of nature; but the increase of parenchyma, the augmentation of its dimensions are always antecedent to this. Whilst all inorganic bodies increase by the addition of particles, there is here at first an expansive force, from which length and breadth arise, afterwards substances are exhaled into the parenchyma, which lengthen and widen it.
By what mechanism is it, that each organ draws the materials of its nutrition from the blood, the common source? This depends entirely upon the organic sensibility peculiar to each, which places it in relation to this or that substance and not to another, and which makes it appropriate it to itself, is penetrated by it, and suffers it to enter its vessels on all sides while it draws back and contracts, to prevent what is foreign to it, from being introduced into its texture.
After this substance has continued for some time to form the organ, it then becomes foreign to it and heterogeneous; by remaining longer it would be injurious; it is absorbed and thrown out by the different emunctories; a new substance of the same kind, which is brought by exhalation, takes its place. Each organ is then constantly in a state of composition and decomposition; but this composition and decomposition vary in their proportion. The predominance of the first over the second, constitutes growth. Their equilibrium establishes the stationary state of the body, which is the case with the adult. When the activity of the second is greater than that of the first, then decrease and decrepitude follow.
Such is, in short, the manner in which the general theory of nutrition should be considered, a theory which I shall explain at length in my physiology, and upon which I will now offer a few words, to show that it is not a system formed by accident, but that it rests upon the laws of the economy, and upon its organic phenomena. Now I think that this assertion will be demonstrated, if I prove, 1st. the uniformity of the parenchyma of nutrition; 2d. the variety of the nutritive substances; 3d. the faculty which the parenchyma of nutrition has of appropriating to itself, according to the quantity of its organic sensibility, this or that nutritive substance, to the exclusion of others, of afterwards throwing out this substance, and of taking new. These are in fact the fundamental principles of this theory.
I say in the first place, that the parenchyma of nutrition is the same for all the organs, and that it is an assemblage of red vessels, of exhalants, of absorbents, of cellular texture, and of nerves; these are the proofs. 1st. These different organs are met with in all the others, as I have observed before, anatomy shows them every where, between each fibre, each layer, each point, if I may so say; they are truly the common organs. 2d. When we take away from the organs their different nutritive substances, for example, from the bones the phosphate of lime by acid, and the gelatine by boiling, there is a residue which is evidently cellular and vascular. 3d. There is no doubt but that the mechanism of the union of divided parts is the same as that of their natural nutrition. Now in the healing of wounds, the parenchyma of nutrition is first developed, and is every where the same; every where fleshy points appear, which are cellular and vascular, which have the same appearance and same character, whether they arise from a bone or a cartilage, a muscle, the skin, a ligament, &c. All wounds, in healing, like the organs, resemble each other in their parenchyma; they differ also like the organs, in the nutritive substance that is afterwards deposited in its texture, substances which vary according to the part where the wound happens to be; thus the deposit of the phosphate of lime gives to the callus a different character from that of muscular wounds, which are united by the exhalation of fibrin in the fleshy points that first arise upon the divided surfaces, &c. 4th. The mucous substance which forms the body of the embryo, appears to be nothing but cellular or mucous texture, as Bordeu calls it, which is abundantly supplied with vessels and nerves. In fact, when the organs are developed in this mucous substance, it may be seen in their interstices for a certain length of time, and exhibits there the same appearance as the body of the embryo in the first periods; gradually this substance becomes condensed, is filled with cells, and assumes the form of cellular texture; whence it may be presumed, that in this mucous state of the embryo, there is only the nutritive parenchyma of the organs; and as the parenchyma is the same in all, it is evident that the mass of the embryo must be homogeneous. Nutrition commences, and then each organ appropriates to itself the substance which is proper for it; after this it ceases to be homogeneous. From these considerations, it becomes easy to admit the uniformity of the parenchyma of nutrition, and its cellular, vascular and, in certain cases, nervous texture.
I am aware, that by admitting this common parenchyma of nutrition, it becomes necessary that it should be nourished itself, and consequently that we must go farther back; but in physiology, the art of finding the truth consists, in searching for it in secondary causes; here facts and experiments enlighten our way, beyond that, imagination only is our guide.
After having demonstrated that the organs resemble each other in a common parenchyma of nutrition, it is unnecessary to prove that they differ by the substances that are deposited there. Animal chemistry has within a few years past so much elucidated this point, that it is not worth while to waste time in refuting what has been written upon the identity of the nutritive juice.
In fine, it is easy to conceive, how each parenchyma of nutrition appropriates to itself according to the quantity of organic sensibility it enjoys, the nutritive substances that are proper for it, and which are brought to it by the circulation. It is not a phenomenon peculiar to nutrition; it is observable in all the acts of the organic economy. Thus the secretions take place only in consequence of the determined quantity of this sensibility, which, placing each gland in relation with the fluid that it should separate, makes it receive this fluid, and reject the others; thus the red part of the blood does not ordinarily pass into the exhalants, because the serous part is alone in relation with their organic sensibility; thus the substances that pass the intestines, do not stop in the biliary or pancreatic ducts, although their diameter is sufficient to admit them; thus cantharides are exclusively in relation with the sensibility of the kidneys, mercury with that of the salivary organs, &c. &c.
We see from this, that the mechanism by which the parenchymas of nutrition appropriate to themselves nutritive substances, is not an insulated phenomenon, but a consequence of a general law of organic sensibility. But why has this property as many degrees as there are organs in the economy? Why do these degrees establish relations so different between the organs and the substances that are foreign to them? Let us stop here; let us be contented with proving this fact by a great number of examples, without trying to discover the cause. We could offer nothing but conjectures upon this subject.
These few notions upon the nutritive phenomena, though indirectly connected with the subject of this volume, are not misplaced here; because in these phenomena, the generative systems upon which we are going to treat, perform the greatest part, and because we shall frequently have occasion to refer to them in the examination of the development of the organs, the development that authors have only vaguely examined, upon which the most exact and the most judicious of all physiologists, Haller, has only slightly glanced, but which however ought to receive the particular attention of physicians, of those especially who wish to consider diseases under the essential relation of the influence that age has upon them.