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in it, be the active agent concerned in the nutrition, the utmost that can be admitted is, that one part of the elements may be more, another less, subjected to their influence; but still it must essentially be a common and similar influence which they experience. That this is no unreasonable requirement, that a certain dependency of definite territories of tissue upon definite vessels must undoubtedly be admitted, the most beautiful illustrations are afforded us in the doctrine of metastases, in the study of the changes which are effected by the occlusion of single capillary vessels, and with which we have become acquainted from the history of capillary embolia. In such cases, in fact, we see that a whole portion of tissue, as far as its immediate connection with a vessel extends, in its pathological relations also constitutes a whole—a vascular unity. But this vascular unity to a finer apprehension still appears a compound, and it is not sufficient to split up the body into vessel-territories (Gefassterritorien) alone, but within them a further division must be made into cell-territories (Zellenterritorien).
This view has, I think, been essentially furthered by our having discovered, as I lately pointed out to you (p. 48), the existence of a special system of anastomosing elements in the connective tissues, and by our having in this manner filled the place of the vasa serosa (which the older writers imagined as a complement to the capillaries for these ultimate purposes of nutrition), with something definite, by means of which the circulation of nutritive juices is rendered possible in parts which are in themselves poor in vessels. To keep to bone, we should scarcely be justified in assuming the existence of vasa serosa in it. The hard basis-substance is throughout uniformly filled with calcareous salts, so uniformly indeed, that no interval can be perceived between the individual calcareous particles. Though some few writers have assumed that little granules can be distinguished in it, this is an error. The only differentiation which can be seen is caused by the prolongation into the
basis-substance of the canaliculi, which all ultimately lead back to the bodies of the bone-cells (bone-corpuscles) and in their turn give out branches. The peripheral extremities of these little branches or processes extend right up
to the surface of the vascular (medullary) canal. They are therefore inserted exactly where the membrane of the vessel begins (Fig. 35), for they can be distinctly perceived
Fig. M. Section of an osseous plate from the arachnoid of the cerebrum, but quite normal in its structure. A branching vascular (medullary) canal is seen with canaliculi opening into it, and leading to the bone corpuscles. 350 diameters.
as very minute orifices upon the wall of the canal. Now since the different bone-corpuscles are in their turn distinctly connected with one another, means are afforded by which a certain quantity of juice taken up from the surface of the vascular canal is not diffused throughout the whole mass of tissue, but confined to these delicate, continuous, and specially provided channels, and forced to move onwards in canals which are inaccessible to injections from the vessel. For a time it was believed that the canaliculi could be injected from the vessel, but this is only possible when the vascular canal has become empty by maceration.
This is a condition precisely similar to what we observe in the teeth, in which the canaliculi can be injected from the pulp-cavity when empty. If a solution of carmine be injected into this cavity, the dental canaliculi are displayed in the form of numerous tubules running up to the surface side by side in a radiated manner. The substance of the teeth also forms a tolerably broad layer of non-vascular material. Vessels are found nowhere but in the pulpcavity, in proceeding from which outwards we find nothing but the proper substance of the tooth (dentine) with its system of tubes, which extend nearly up to the surface, and in the root of the tooth are directly continuous with a layer of real bony substance (cement) the corpuscles of which are seated upon the ends of the tubes. A provision for the conveyance of the juices similar to that which in bone originates in the marrow, here takes its rise in the pulp, whence the nutritive fluid can be conveyed up to the surface by the means of tubes.
These systems of tubes which are found in such a very marked form in bone and the teeth, are to be seen with far less distinctness in the soft structures, and it is chiefly for this reason, I imagine, that the analogy which exists between the soft connective tissues and the hard texture of bone has not been clearly comprehended. These systems are
CANALS IN THE SEMI-LUNAR CARTILAGES. 87
most distinctly seen in parts which are more of a cartilaginous nature, as, for example, in fibro-cartilage. But it is a fact of great significance that we find a series of transitional forms between cartilage and the other connective tissues, in which the same conditions are constantly repeated. In the first place, parts which chemically belong to the class of cartilages, for example, the cornea, which yields chondrine when boiled, although nobody regards it as real cartilage. But more striking is the arrangement in those parts in which the external appearance speaks in favour of a cartilaginous nature, but the chemical properties do not correspond, as for example in the semi-lunar cartilages (Bandscheiben) of the knee-joint, which are interposed between the femur flG 3G
and tibia for the purpose of protecting the articular cartilage from too violent contact. These parts, which even now are generally described as cartilage, yield no chondrine on boiling, but gelatine; and yet in this hard connective tissue, we meet with the same system of anastomosing corpuscles that pre: vailsin the cornea and in fibrocartilage, and it is displayed with unusual distinctness and clearness. Vessels are almost entirely wanting in these cartilages, but in exchange they contain a system of tubes of rare beauty. On making a section, we see that the
Fig. 36. Section from the semi-lunar cartilage of the knee-joint of a child. a. Bands of fibres, with spindle-shaped, parallel and anastomosing cells (seen in longitudinal section), b. Cells, forming a network, with broad, branching, and anastomosing canaliculi (seen in trans verse section). Treated with acetic acid. 350 diameters.
whole is in the first place mapped out into large divisions, exactly like a tendon; these are subdivided into smaller ones, and these are pervaded by a fine, stellate system of tubes, or, if you will, of cells, inasmuch as the notion of a tube and that of a cell here quite coincide. The networks of cells which here form the system of tubes, terminate externally in the septa bounding the individual divisions, and we here see in close proximity considerable collections of spindle-shaped cells. In these cartilages, too, the whole mass of tissue is only connected by its exterior with the circulatory system; everything that penetrates into the interior must pass by a very circuitous route through a system of canals with numerous anastomoses, and the nutrition of the internal parts is altogether dependent upon this mode of conveyance. The semi-lunar cartilages are structures of considerable extent and great density, and, as they are entirely dependent for their nutrition upon this ultimate, minute system of cells, we have in them, much more than in cartilage, to deal with such an arrangement for the supply of nutritive juices, as'cannot be under the direct control of the vessels.
For the sake of elucidation, I will merely add that the ultimate elements are seen to consist of very delicate cells, which are prolonged into fine filaments, that in their turn ramify, and look when cut across like small points in which a clear centre can be recognised. The filaments can ultimately be very distinctly traced back to the common cell, just as in bone. They are extremely fine tubes which are intimately connected with one another, only that here they are in certain spots collected into large groups, by means of which the conveyance of the nutritive juice is principally effected, and that the intercellular substance in no instance becomes infiltrated with lime, but always preserves its character as connective tissue.