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the capillary network into the intralobular vein, whence, by means of the hepatic veins, it is conducted back again to the heart. Now, in the case of an injected liver, this network is seen to be so close that what interstices there are left seem almost to occupy less room than the vessels themselves. We can thus easily imagine how the older anatomists, such as Ruysch, came to be led by their injections to the supposition that nearly every thing in the body was made up of vessels, and that the different organs were only distinguished by differences in the arrangement of their vessels. But just the opposite to what is observed in an injected preparation does the proportion between vessel and tissue appear to be in an ordinary specimen from a liver. In this the vessels are scarcely perceptible. A similar network is indeed seen, but it is the network formed by the hepatic-cells (Fig. 27), which, closely crowded one against the other, fill up all the interspaces of the vessels. It is -plain, therefore, that the capillary and hepatic-cell networks are interwoven in the most intricate manner, so that cells belonging to the parenchyma of the liver everywhere lie in almost immediate contact with the walls of the vessels, there being at most a fine layer between the cells and the walls, concerning which it is still a matter of dispute amongst histologists whether it is to be regarded as a peculiar coat, constituting the finest gall-ducts, or only as a very small quantity of connective tissue accompanying the vessels.
In this extremely simple case, a tolerably simple relation may certainly be assumed to exist between the vessels and the cells; it may be conceived that the blood which flows through the vessels may, in proportion to the degree in which they are contracted or dilated, and to its own quantity, exercise a direct influence upon the adjoining cells. It might indeed be objected, with regard to the conditions of nutrition, that we have here to deal with quite a pecu
liar arrangement of the vessels, which are essentially of a venous nature, as being composed of ramifications of the portal and hepatic veins, but the hepatic artery also enters into the formation of this capillary network, so that the blood in it cannot be resolved into its individual arterial and venous constituents. Injections from each of the vessels named ultimately find their way into the same capillary network.
In most parts, however, the relations do not present such a simple form as in the liver; considerable interspaces often separate the individual cells, and no inconsiderable quantities of these elements are enclosed in every capillary mesh. I shew you here a second object derived from a fresh human brain—from a lunatic who died with his cerebrum in a highly hypenemic state. The section
has been made through the corpus striatum, which was of a deep red colour. You have a good view of the naturally
Fig. 29. Natural injection of the corpus striatum of a lunatic, a, a. Gaps destitute of vessels, and corresponding to the strands of nervous fibres which traverse the ganglion. SO diameters.
injected vessels; and the width of the individual meshes of the capillary network may be clearly seen. The section has been carried transversely through the corpus striatum, and at certain intervals large, roundish spots may be distinguished, which appear dark by transmitted light (Fig. 29, a, a, a), but by reflected light and to the naked eye look white, and are formed by transverse sections of the nervous fibres which run in long strands towards the spinal marrow. The vessels scarcely penetrate into them. The rest of the mass, on the other hand, consists of the proper grey substance of the corpus striatum, within which a vascular network with very fine meshes is distributed, the grey substance of the nervous centres being everywhere, both in their interior and in their cortical substance, distinguished from the white by its greater vascularity. A few large vessels are observable in the object, giving off branches, the ramifications of which continually diminish in size, until at last they terminate in capillary networks with very fine meshes. Still, however close this network may be, every element of the substance of the brain by no means comes into immediate contact with a capillary vessel.
The third object is a very slightly magnified injected pI0 30 preparation from the mus
cular coat of the stomach, in which, with a high power, the direction of the muscular fibres is indicated by fine longitudinal striae; here the vessels form tolerably regular networks, connected with one another by transverse anastomoses, and splitting up into
Fig. 30. Injected preparation from the muscular coat of the stomach of a rabbit, magnified eleven diameters.
VESSELS IN CARTILAGE. 77
smaller and smaller vessels, which form fine networks within the tissue, so that the whole of it is by this means mapped out into a series of irregularly four-sided divisions. To each of the ultimate intervascular spaces is allotted a certain number of muscular elements, so that the vessels are in some parts in contact with the muscular fibres, whilst in others they lie at a greater distance from them.
If we go on in this way examining the structure of the different organs and tissues, we pass from such as, when injected, seem to consist almost entirely of vessels, in time to those which contain scarcely any, and at last to such as really have none at all. This is most strikingly the case with the connective tissues, and the most important amongst these are bone and cartilage. Perfectly developed cartilage has no longer any vessels at all; perfectly developed bone certainly contains vessels, but in a very variable degree. That perfectly developed cartilage contains no vessels, you will not, I suppose, call upon me to convince you by any additional, special proofs, inasmuch as you have seen various preparations of cartilage, in which not a trace of them was to be observed. (Figs. 6, 9, 22.) I now place before you a piece of young cartilage, because you can see in it what the arrangement of the vessels in cartilage is at an earlier period. It is a section from the calcaneum of a new-born child, and in it the vessels run up from the already-formed central osseous mass into the cartilage which still remains. The preparation shews along the outermost surface of the cartilage the transition from it into the perichondrium, whilst the lower part of the section is taken from the border of the already-formed bone. From this part large vessels are seen running up and terminating in the middle of the cartilage by the formation of loops and plexuses, as it were a tree of villi (Zottenbaum) in the cartilage, and very much resembling a villus of the chorion of the ovum. In fact, the vessels mount up into the cartilage from the nutrient artery of the bone, but only to a certain height. There they form real loops, and at length break up into a
fine plexus of capillaries, out of which veins are ultimately formed, and run out again pretty near the spot where the artery entered. But the whole of the rest of the mass consists of non-vascular cartilage, the corpuscles of which, with a low power, look like fine points. Thus there is a whole host of cartilage-corpuscles lying between the terminal loops and the external surface, and the whole of this layer is therefore dependent for its nutrition upon the juice which exudes from the terminal loops and permeates the tissue, though to a trifling extent also upon the materials which the scanty vessels of the perichondrium
Fig. 31. Section of cartilage from the calcancum of a new-born child. C. The cartilage, with its cells indicated by fine points. P. Perichondrium and adjoining fibrous tissue, a. Inferior border very near to the line of junction between the cartilage and the bone, with the vascular loops ascending from the nutrient artery, b, b. Vessels which make their way through the perichondrium in the direction of the cartilage. 11 diameters.