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VASCULAR CANALS OF BONE.

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present the same structure, but is arranged upon another, and independent, plan. Upon more accurate examination it is seen to be formed of little columns, which for the most part are perpendicular to the long axis of the bone, and are disposed in a sort of arch parallel to the long axis. These are the remains of the spicula first formed during the growth of the bone in thickness and are therefore of older date.

As in the sections which are obtained by grinding down bone, the vessels themselves cannot for the most part any longer be distinguished, the cavities [Haversian canals] (Figs. 32, a, 33, a, v,) in which they run have been named medullary canals, improperly, inasmuch as there is usually no marrow contained in these narrow channels; they should properly be called vascular canals; still the other term is so

FIG. 34.

universally received, that it is even employed in cases where the wall of the vessel is in immediate contact with the

Fig. 34. Bone-corpuscles from a morbid formation of bone in the dura mater of the brain. Their branching and anastomosing prolongations (canaliculi) are seen, as well as minute spots upon their walls, marking the funnel-shaped commencements of the canaliculi. 600 diameters.

internal surface of the cavity. Immediately surrounding these canals we see a series of peculiar structures; oblong or roundish bodies which usually appear black when the object is not fully brought into focus, and are provided with jaggs or processes. They used to be called bone-corpuscles, and their processes bone-canals (canaliculi ossei); and as the view was originally entertained that the calcareous matter was really deposited in them, and that the dark appearance which they usually present when viewed by transmitted light resulted from the presence of this matter, the canals were also termed canaliculi chalicophori, a name which has now been altogether abandoned, because convincing proofs have been obtained that, so far from being contained in them, the lime is, on the contrary, diffused throughout the homogeneous basis-substance which lies between them.

As soon as this discovery was made, that, namely, the distribution of the lime in the osseous tissue took place in a manner just the reverse of that in which it had been supposed it did, the other extreme was immediately run into, and for the name of bone-corpuscles that of bone-cavities (lacunæ) was substituted, and it was assumed that bone contained nothing but a series of empty cavities and canals, which were indeed penetrated by a fluid, but still were really nothing more than fissures in the bone. Some few observers indeed actually called them bone-fissures. Now I have endeavoured to demonstrate in various manners that they are real corpuscles, and not mere cavities in a dense basis-tissue, but structures provided with special walls and boundaries of their own, which separate them from the intermediate substance. For by the help of chemical reagents (concentrated mineral acids, and particularly hydrochloric acid) we are enabled, by dissolving the basissubstance, namely, to disengage the corpuscles from it. In this way we furnish, I think, the most complete demonstration that they are really independent structures. Besides,

DEPENDENCE OF TISSUES UPON THE VESSELS. 83

a nucleus may be distinguished within these bodies; and, even without entering into the history of their development, we discover that here too we have once more to deal with cellular elements of a stellate form. Bone therefore exhibits in its composition a tissue, containing, in an apparently altogether homogeneous basis-substance, peculiar, stellate bone-cells distributed in a very regular manner.

The intervals which exist between every two of the vessels in bone are often very considerable; whole systems of lamellæ, beset with numerous bone-corpuscles, thrust themselves in between the medullary canals. Here it is certainly difficult to conceive the nutrition of so complicated an apparatus to depend upon the action of vessels some of them so remote, and especially so, to understand how every individual particle of this extensive compound mass can manage to maintain a special relation of nutrition to the vessels. For experience shows us that every single bone-corpuscle really possesses conditions of nutrition peculiar to itself.

I have laid these details before you, in order to point out to you the gradual transition which takes place from the vascular and abundantly vascular, to the scantily vascular and non-vascular parts. If we would form a simple conception of the conditions of nutrition, I think we must lay it down as a logical principle, that whatever is enunciated with regard to the nutrition of very vascular parts, must also hold good for that of scantily and nonvascular parts; and that, if the nutrition of individual parts is considered to be directly dependent upon the vessels or the blood, it must at all events be demonstrated that all the elements which stand in immediate connection with one and the same vessel, and are assigned to a single vessel for their support, present conditions of life essentially similar. In the case of bone, it would be necessary to show that every system of lamella which has only one vessel for its nutrition, always exhibits a similar state of nutrition. For if that vessel, or the blood which circulates

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 (Gefässterritorien) 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

NUTRITION OF BONE.

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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

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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. 35. 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.

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