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logous ones may accidentally become very injurious, but still they do not possess what can properly be called a destructive (in the unscientific and traditional sense of the word), or malignant character. On the other hand every kind of heterologous formation, whenever it has not its seat in entirely superficial parts, has a certain degree of malignity clinging to it. And even superficial affections, though entirely confined to the most external layers of epithelium, may gradually exercise a very prejudicial influence. Let us only reflect what happens when a large surface of mucous membrane continually secretes, and heterologous products are constantly engendered upon it which do not become persistent epithelium, but continually keep flowing down from the surface of the mucous membrane. In such a case, in addition to the blennorrhoea (and its consequences, anaemia, neuralgia, &c.), we find erosions.

It seems to me important that I should bring before you a definite example of the mode in which destruction in its more obvious forms is effected, in order that you may see how it leads to ulceration and to the formation of cavities in the interior of parts. It does indeed appear like a contradiction to say that a process, which produces new elements, destroys, but this contradiction nevertheless is merely a seeming one. If you imagine in a part, which had previously been firm, a new-formation to arise of which the individual constituents are loose and easily moveable one upon the other, the process will of course always be attended by a very important change in the usefulness of the part. The simple conversion of bone into medullary tissue (pp. 409, 410) may become the cause of great fragility in the bones, and osteomalacia [mollifies ossium] essentially depends upon nothing else than the conversion of compact osseous substance into medullary tissue. An excessive formation of medullary spaces gradually advances from the interior of the bone towards the surface, deprives

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the bone of its firmness, gives rise to a tissue in itself quite normal, but of no service in maintaining the necessary firmness of the parts, and thus in some sort inevitably leads to a loss of cohesion. Marrow is an extraordinarily soft tissue, which in those conditions, where it is red and rich in cells, or atrophied and gelatinous, becomes nearly fluid. From marrow to perfectly fluid tissues is only a short step, and the boundaries separating marrow and pus cannot in many places be assigned with any degree of certainty. Pus is in our eyes a young tissue, in which, amidst the rapid development of cells, all solid intercellular substance is gradually dissolved. A single connective-tissue cell may in an extremely short spsice of time produce some dozens of pus-cells, for the development of pus follows an extremely hurried course. But the result is of no service to the body, proliferation becomes luxuriation. Suppuration is a pure process of luxuriation, by means of which superfluous parts are produced, which do not acquire that degree of consolidation, or permanent connection with one another and with the neighbouring parts, which is necessary for the existence of the body.

If now in the next place we investigate the history of suppuration, we immediately discover that we must distinguish two different modes of pusformation, according namely as the pus proceeds from tissues of the first two kinds mentioned in our classification (p. 28), i. e.,from epithelium, or from connective tissue. Whether there are also forms of suppuration proceeding from a tissue of the third class, from muscles, nerves, vessels, &c, is at least doubtful, because of course the elements of connective tissue which

Fig. 136. Interstitial purulent inflammation of muscle in a puerperal woman. m, m. Primitive muscular fibres. i, i. Development of pus-corpuscles by means of the proliferation of the corpuscles of the interstitial connective tissue. •280 diameters.

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enter into the composition of the larger vessels, the muscles and the nerves, must be eliminated from the really muscular, nervous and vascular (capillary) elements. With this reservation we can for the present only maintain the possibility of two.modes of pus-formation.

As long as the pus is formed out of epithelium, it is naturally produced without any considerable loss of substance and without ulceration. But this is in every instance the case, where pus is produced in connective tissue. The real state of the matter therefore is exactly the reverse of what it was previously imagined to be, when a solvent property was ascribed to pus. Pus is not the dissolving, but the dissolved, i. e., the transformed, tissue. A part becomes soft, and liquefies whilst suppurating, but it is not the pus which occasions this softening, on the contrary, it is the pus which is produced as the result of the proliferation of the tissue.

The development of pus we daily see upon different surfaces, both on the skin, and on mucous and serous membranes. We can observe its development most surely where stratified epithelium naturally exists. If you follow the development of pus upon the skin, when the process is unaccompanied by ulceration, you will constantly see that the suppuration proceeds from the rete Malpighii. It consists in a growth and development of new cells in this part of the cuticle. In proportion as these cells proliferate, a separation of the harder layers of the epidermis ensues, and they are lifted up in the form of a vesicle or pustule. The place where the suppuration chiefly occurs corresponds to the superficial layers of the rete, which are already in process of conversion into epithelium; if the membrane of the vesicle be stripped off, these (layers) usually adhere to the epidermis and are stripped off with it. In the deeper layers we may watch how the cellular elements, which originally have only single nuclei, divide, how the nuclei become more abundant, and single cells have their

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places taken by several, which in their turn again provide themselves with dividing nuclei. Here too people have generally helped themselves out of the difficulty by assuming that in the first instance an exudation was poured out, which produced the pus in itself, and this is the reason why, as you well know, most investigators into the development of pus especially selected fluids which were secreted from injured surfaces. It was very conceivable that, as long as no doubts were entertained with regard to the discontinuous formation of cells, the young cells should without more ado be looked upon as independent new-formations, and that the notion should be entertained that germs arose in the exuded fluids, and gradually becoming more numerous, supplied the pus. But the matter is on this wise, that, the longer the suppuration lasts, the more certainly is one series of cells after the other in the rete involved in the process of proliferation, and that, whilst the vesicle is rising up, the quantity of the cells which grow into its cavity is constantly becoming greater. When a variolous pustule forms, there is at first only a drop of clear fluid present, but nothing arises in it; it only loosens the neighbouring parts of the rete Malpighii.

Precisely the same is the case with mucous membranes. There is not a single mucous membrane which may not under certain circumstances furnish puriform elements. But here too a certain difference always presents itself. A mucous membrane is all the more in a condition to produce pus without ulceration, the more completely the epithelium it possesses is stratified. All mucous membranes with a single layer of cylindrical epithelium (intestines),1 are much less adapted for the production of pus; that which is produced on them, even though it have quite the appearance of pus, frequently turns out upon close examination to be only epithelium. The intestinal mucous membrane, especially that of the small intestine, scarcely ever produces pus without ulceration. The mucous membrane of the uterus, and of the fallopian tubes, though it is frequently covered with a thick mass of quite a puriform appearance, almost always secretes1 epithelial cells only, whilst on other mucous membranes, as for example on that of the urethra, we see enormous quantities of pus secreted, as in gonorrhoea (Fig. 63) without even the slightest ulceration being present on the surface. This depends essentially upon the presence of several strata of cells, the upper forming a kind of protection to the deeper ones, of which the proliferation is thus for a time secured. The pus is at last either borne away by the production of new masses of pus beneath it, or there occurs simultaneously a transudation of fluid, which removes the puscells from the surface, just as in the secretion of semen the epithelial elements of the seminal tubules furnish the spermatozoa, and in addition a fluid transudes which sweeps them away. But the spermatozoa do not arise in the fluid—this is only the vehicle for their onward movement. In this manner we frequently see fluid exude on the surface of the body, without our being able to regard it as a ej^oblastema. If a proliferation of epithelium simultaneously takes place upon the surface, the elements detached

1 In the air-passages (nose, larynx, trachea, bronchi) we commonly find several layers of cylindrical epithelium lying one above the other —From a MS. note by the Author.

1 Secrete in this and similar places does not of course mean to separate from the blood, but from the (issue itself, whose elements (cells) are separated (detached) at the surface, and, when mixed with a serous effusion from the blood, removed. The detachment of the cells is effected sometimes by means of the fluid which transudes from the blood, sometimes by the continual growth of a succession of new cells beneath them, and sometimes in consequence of their own round form. In desquamation of the cuticle the second of these methods, in several forms of catarrh the third, on many serous membranes, the first, is the one pursued. Any two, or all three of them, however, may of course coincide.— From MS. notes by the Author.

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