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the panniculus adiposus of the skin swell up in consequence of every single fat-cell's absorbing a larger quantity of fat than usual, and when this takes place in thousands upon thousands, nay, we may say, in hundreds of thousands and millions of cells, the result is very obvious and strikes the eye (polysarcia). But it is just as possible for new cells to form in addition to the old ones, and for an increase of size to take place without any enlargement of the individual cells. These are essentially different processes, and may be styled simple and numerical hypertrophy.

Hyperplastic processes (numerical hypertrophy) in all cases produce a tissue similar to that of the original part; hyperplasia of the liver gives rise to new hepatic cells; that of a nerve to new nerve-substance; that of the skin to a fresh production of the elements of the skin. A heteroplastic process, on the contrary, engenders histological elements which correspond, indeed, to natural forms, elements, for example, resembling in structure those peculiar to glands, nerve-substance, the connective and epithelial tissues, but these elements do not arise in consequence of a simple increase in the number of such as previously existed, but in consequence of a change in the original type of the parent tissue. When cerebral matter forms in the ovary, it does not arise out of preexisting cerebral matter, nor through any act of simple cellproliferation; when epidermis springs up in the muscular substance of the heart, however much it may correspond to that on the external surface of the skin, it is, notwithstanding, a heteroplastic structure. When we find hairs quite natural in structure in the substance of the brain, however great the correspondence they exhibit with the hairs of the external surface, they will nevertheless be heteroplastic hairs. In like manner we see cartilaginous tissue arise, without the existence of any essential difference between it and ordinary, familiar cartilage, as, for example, in enchondromata. Still, an enchondroma is a heteroplastic tumour,

DEGENERATIVE NEW FORMATIONS.

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even when occurring in bone, for perfect bone has no longer any cartilage in the parts where the enchondroma forms, and the term cartilage of bone (Knochenknorpel), as a designation for the organic basis of bone, is nothing but a term. It is either from osseous or medullary tissue that the enchondroma springs, and at the very point where real cartilage exists, for example, at the articular ends of the bone, no cartilaginous tumours, in the ordinary sense of the word, arise. It is not, therefore, with an hypertrophy of preexisting cartilage that we have here to deal, but with a genuine new formation, which begins with a change in the local histological type. According to this manner of viewing the subject which is essentially different from that previously current, no attention is therefore paid, in considering the question of the heterologous or homologous nature of a new formation, to the composition of the structure as such, but only to the relations which subsist between it and the parent soil from which it springs. Heterology, in this sense, designates the difference of development in the new, as contrasted with the old, tissue, or, as we are wont to say, a degeneration, a deviation from the typical conformation.

This is, as you will see, also really the most important point upon which we can ground our prognosis. We find tumours, which present the most striking resemblance to the most familiar physiological tissues. An epidermic [epithelial] tumour (Epidermis-Geschwulst) may, as I have already pointed out, in its elementary structure entirely correspond to ordinary epidermis, but in spite of this it is not always a benignant tumour of merely local import, which may be traced to a merely hyperplastic increase in preexisting tissues, for it sometimes arises in the midst of parts which are far from containing epidermis or epithelium, as, for example, in the interior of lymphatic glands, or in that of thick layers of connective tissue, which are at a distance from any surface, and even in bone. In these cases the

formation of epidermis is certainly quite as heterologous as it is possible to conceive anything to be. But practical experience has shown us that it was altogether incorrect to conclude from the mere correspondence of the pathological tissue with a physiological one, that the case would continue to follow a benignant course.

It has been, as I must remark with particular emphasis, one of the greatest and, at the same time, best-founded reproaches which have been levelled against the most recent micrographical doctrines, that, regarding the subject from the certainly excusable point of view, namely, the correspondence between many normal and abnormal structures, they have declared every pathological new formation to be innocuous which exhibits a reproduction of pre-existing and familiar tissues of the body. If what I have communicated to you as my view be correct, namely, that throughout the whole range of pathological growths no structure of an absolutely new form is to be found, but that we everywhere meet with structures which may in one way or another be regarded as the reproduction of physiological tissues, then this point of view falls to the ground. In support of my view, I can at least adduce the fact that I have, in all disputes concerning the innocent or malignant nature of definite forms of tumours, up to the present time always proved to be in the right.

Before we quit the consideration of General Histology, I would invite your attention for a few moments to a few points of primary importance which obtrude themselves upon us on nearly every occasion. Whilst, namely, the animal tissues were being studied in their affinities to one another, questions relating to these affinities were at different times stumbled upon, which gave rise to generalizations that were more of a physiological character.

When Reichert undertook to collect the connective tissues into one, larger group, he set out with this position chiefly,

LAW OF CONTINUITY.

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that the demonstration of the continuity of tissues must be regarded as a decisive proof of their intimate relationship. That as soon as one part could be made out to be continuously (by union, not mere juxtaposition) connected with another, both must be regarded as parts of a common whole. In this manner he sought to prove that cartilage, periosteum, bone, tendons, fasciæ, &c., really formed a continuous mass, a kind of basis-tissue (Grundgewebe) for the body, a connective substance, which had only experienced certain changes in these different localities, without their being, however, of such a nature as to destroy the character of the tissue as such. This so-called law of continuity soon suffered the most violent shocks, and quite recently such a terrible breach has been made in it, that it can scarcely any longer be possible to derive therefrom any general criterion for the determination of the nature of a tissue. On the one hand, namely, new facts have been continually brought forward in support of the continuity of such histological elements as, according to Reichert, would be separated toto cælo from one another, as, for example, of epithelial and connective tissue; and there has been a continually increasing mass of evidence in support of the assertion that cylindrical epithelium is capable of becoming elongated into fibres, which in the shape of filaments anastomose with connective-tissue corpuscles. Nay, it has been quite recently asserted by a whole series of observers that these superficial cells are prolonged inwardly, and then enter into direct. connection with nerve-fibres. With regard to this last point, I must confess that I am not yet convinced of the correctness of the representation; but with respect to the former one, that is a matter which probably will end in the demonstration of the real continuity of the elements. It would seem, therefore, that it is even now no longer possible to mark out the exact limits which divide every kind of epithelium from every kind of connective tissue, but only

where scaly epithelium is met with, whilst the limits are doubtful wherever cylindrical epithelium exists.

Just in the same manner elsewhere also do the boundary lines become obliterated. Whilst formerly the limits which separate the elements of muscle from those of tendon were considered to be most distinctly defined, extremely decisive proofs have in this case also been afforded, and first by Hyde Salter and Huxley, that fibres proceed from connective-tissue corpuscles, which, whilst pursuing their course in an inward direction, all at once assume the character of transversely striped muscle. So, then, in the case of connective tissue, it would seem there exists a continuous connection between the elements of the surface and the more highly developed ones of the deeper parts. Now if, on the other hand, it has turned out to be very probable that the corpuscles of connective tissue have definite relations to the vascular system, we are, as you see, almost justified in regarding this tissue as a kind of neutral ground for parts to meet upon (indifferenter Sammelpunkt), as a peculiar arrangement for their intimate connection, an arrangement which, though certainly not exercising any great influence upon the higher functions of the animal, is yet of great importance as far as its nutrition is concerned.

In the place of the law of continuity, therefore, we must necessarily put something else. And here, I think, the doctrine which has the strongest claims to our attention is that of histological substitution. In the case of all tissues of a like nature it is quite possible, even whilst confining our attention to what occurs physiologically in the various classes of animals, to find one tissue at a certain fixed point of the body replaced by an analogous one belonging to the same group, or, in other words, by an histological equivalent.

A spot invested with cylindrical, may acquire scaly, epithelium. A surface upon which cilia were originally seen,

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