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appears between them. This is the form which we see most beautifully shown in hyaline cartilage, as in that lining the joints, for example, in which the intercellular matter is perfectly homogeneous, and we see nothing but a substance which, though, perhaps, slightly granulated here and there, is on the whole quite as clear as water, so that as long as we do not see the edges of the preparation doubt may arise as to whether anything at all exists between the cells.

This substance is characteristic of hyaline cartilage. Now we find that, under certain circumstances, the round cells became even in cartilage transformed into oblong spindle-shaped ones, as, for example, with great regularity in the immediate neighbourhood of the articular surfaces.

FIG. 22.

a

The nearer, in the examination of articular cartilage, we approach to the free surface (Fig. 22, a,) the smaller do the cells become; and, at last, nothing more is seen but small, flatly lenticular bodies, the substance intervening between which sometimes presents a slightly striated appearance. Here, therefore, without the tissue's having ceased to be cartilage, a new type displays itself, which we much more regularly meet with in pure connective tissue, and hence the idea might easily arise that articular cartilage is invested with a special membrane. This is, however, not the case, for there is no synovial membrane spread over the cartilage, but its boundary towards the cavity of the joint is everywhere formed of cartilage itself. The synovial Fig. 22. Perpendicular section through the growing cartilage of a patella. a. The articular surface, with spindle-shaped cells (cartilage-corpuscles) disposed in layers parallel to it. b. Incipient proliferation of the cells. c. Advanced proliferation; large, roundish groups-within the enlarged capsules a continually increasing number of round cells. 50 diameters.

[graphic]

CARTILAGE. MUCOUS TISSUE.

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membrane only begins where the cartilage ceases-at the edge of the bone. On the other hand, we see that at certain points the cartilage passes directly into forms in which the cells become stellate, and the way is paved for their final anastomosis; ultimately, spots are met with at which it is no longer possible to say where the one cell ends and the other begins, inasmuch as they communicate so directly one with another that it is impossible to detect a line of separation between their membranes. When such a case occurs, the cartilage, which up to that time had remained hyaline and homogeneous, becomes heterogeneous and striated, and has long since been called fibro-cartilage.

From these forms a third has been distinguished, the so-called reticular. [yellow or spongy] cartilage, as seen in the ear and nose, in which the cells are round, but encircled by a peculiar kind of thick, stiff fibres, whose mode of production has not yet been thoroughly made out, but they are, perhaps, derived from the metamorphosis of the intercellular substance.

Under these different types, presented by cartilage in its different localities, all the different aspects which the other connective tissues offer are included. There is also true connective tissue with round, long, and stellate cells. Just in the same manner we find, for example, in the peculiar tissue which I have named mucous tissue (Schleimgewebe), round cells in a hyaline, or spindle-shaped ones in a striated, or reticular ones in a meshy, basis-substance. The only criterion we possess for distinguishing them consists in the determination of the chemical constitution of the intercellular substance. Every tissue is called connective tissue whose basis-substance yields gelatine when boiled; the intercellular substance of cartilage produces chondrine; mucous tissue, on expression, a substance, mucin, precipitable by acetic acid, and insoluble in an excess of it,

though dissolving in muriatic acid when added in considerable quantity.

Besides these, a few solitary points of difference in regard to peculiarity of form and contents may be presented by individual cells at some later period of their existence. What we concisely designate fat is a tissue which is intimately connected with those of which we have been treating, and is distinguished from the rest by the fact that some of the cells enlarge and become stuffed full of fat, the nucleus being thereby thrust to one side. In itself, however, the structure of adipose tissue is precisely the same as that of connective tissue, and, under certain circumstances, the fat may so completely disappear that the adipose tissue is once more reduced to the state of simple, gelatinous connective, or mucous tissue..

Amongst these different species of connective tissue the most important for our present pathological views, are, generally speaking, those in which a reticular arrangement of the cells exists, or, in other words, in which they anastomose with one another. Wherever, namely, such anastomoses take place, wherever one cell is connected with another, it may with some degree of certainty be demonstrated that these anastomoses constitute a peculiar system of tubes or canals which must be classed with the great canalicular systems of the body, and which particularly, forming as they do a supplement to the blood- and lymphatic vessels, must be regarded as a new acquisition to our knowledge, and as in some sort filling up the vacancy left by the old vasa serosa which do not exist. This reticular arrangement is possible in cartilage, connective tissue, bone and mucous tissue in the most different parts; but in all cases those tissues which possess anastomoses of this description may be distinguished from those, whose elements are isolated, by the greater energy with which they are capable of conducting different morbid processes.

LECTURE III.

FEBRUARY 20, 1858.

PHYSIOLOGICAL AND PATHOLOGICAL TISSUES.

The higher animal tissues: muscles, nerves, vessels, blood.

Muscles.-Striped and smooth.-Atrophy of.-The contractile substance and contractility in general.—Cutis anserina and arrectores pili. Vessels. Capillaries.-Contractile vessels.-Nerves.

Pathological tissues (Neoplasms), and their classification.-Import of vascularity. Doctrine of specific elements.-Physiological types (reproduction). -Heterology (heterotopy, heterochrony, heterometry) and malignity.Hypertrophy and hyperplasy.-Degeneration.-Criteria for prognosis. Law of continuity.-Histological substitution and equivalents.-Physiological and pathological substitution.

IN my last lecture I portrayed to you the first two groups of tissues, the one embracing epithelium or epidermis, and the other the different kinds of connective tissue. What still remains forms a somewhat heterogeneous group, the individual members of which do not, indeed, in the degree that is the case with epithelium and connective tissue, bear a real relationship to one another, yet, on the whole, present a certain correspondence, in that they constitute the higher animal structures, and are distinguished by their specific mode of development from the less highly organized epithelial and connective tissues. Moreover, most of them appear under the form of connected, more or less tubular, structures. If a comparison be instituted between muscles, nerves, and vessels, the idea very readily suggests itself that we have in all three structures to deal with real tubes, filled with now more, now less, moveable contents. But this notion, however well it may accord with a superficial view of the matter, does not express the whole truth, inas

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much as we cannot compare the contents of the different tubes.

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The blood, which is contained in the vessels, cannot, at least at present, be regarded as analogous to the axiscylinder, or the medullary [white] substance of a nervetube, or to the contractile substance of a primitive muscular fasciculus (Muskelprimitivbündel [muscular fibre]). must, indeed, here remark, that the original development of all the structures which may be included in this group is still a subject of great controversy, and that the view maintaining the simply cellular structure of most of these elements is by no means completely established. This much, however, appears to be certain, that, at any rate in foetal parts, the blood-corpuscles are just as much cells as the individual constituents of the walls of the vessels within which the blood flows; and that the vessel cannot be designated as a tube which invests the blood-corpuscles, as the cell-membrane does its contents. It is therefore necessary in the case of the vessels to draw a line between their contents and proper walls, and to repudiate the seeming resemblance between the vessels, and the nerves and muscular fibres. Again, if we wished to adopt the mode of origin of the several tissues as the basis of our classification, we should, in accordance with prevailing views, have to associate the lymphatic glands also with the blood, and might be rather reminded of a connection such as we have seen to exist in the relations between the epidermis and the rete mucosum. But here I must once more impress upon you that the lymphatic glands are distinguished from glands properly so called, not only by their not possessing any excretory duct in the ordinary sense of the word, but also because from the mode of their development they by no means occupy the same position as ordinary glands, but are on the contrary at every period of their existence nearly allied to the connective tissues, and that,

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