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nearly constantly taken place there, so that it lies in rows between the primitive muscular fasciculi, and thereby produces a striation which looks yellowish to the naked eye, and is due to an arrangement very similar to that which gives rise to the red striation of genuine muscular tissue.1 This is precisely how matters stood in the case I spoke of recently (p. 824, Fig. 108), where we found a row of fat-cells between every two primitive fasciculi; the yellow that you saw there, was not altered muscle, but a mass of fat which had grown in between the muscular fibres. But in addition to such interstitial adipose tissue there is in the case now before us a parenchymatous degeneration in the same muscle; the substance of the muscle is also really in a state of fatty degeneration. The degenerated fibres are, however, only to be seen with the naked eye in the lower parts of the muscle, whilst the portion which lay in immediate contact with the greatest projection of the thorax and had been subjected to the greatest tension, to the naked eye presents no trace of muscular tissue. Under the microscope, however, we even there find isolated muscular fibres lying close to one another and still distinctly transversely striated, and others plentifully filled with fat. You see, therefore, that these are two different conditions; the one form, where the muscle is interrupted in the course of its primitive fasciculi by degenerated places,andwhere therefore the same primitive fasciculus, is, as it pursues its course, now in a state of degeneration, now preserved in all its integrity; the other form in which the disease sweeps along the primitive fasciculus, and this undergoes the change in its whole extent at once, and where

1 For, as each row of fat-cells lies between two primitive fasciculi (Fig. 108), the fat (like the substance of the fasciculi, the syntoniue) has a layer of sarcolemma upon each side of it, so that, if the syntonine atrophies, the fat appear' to have taken its place and to lie within the primitive fasciculi, and many wellknown authors have taken this to be the case.—From a MS. note by the Author.

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therefore normal and degenerated fasciculi lie side by side, and may alternate with one another.

Here is another specimen from a young female (who died shortly after menstruation in consequence of a burn) in which you will find a very beautiful corpus luteum in the ovary. I lay it before you because you will be able to see, from it, how obviously fatty metamorphosis may display itself to the unaided eye. The incision into the ovary has been made perpendicularly to the surface at a point, where a little prominence and slight rent upon the surface mark the place, at which the ovule has emerged (Fig. 115, B). From the point in the tunica albuginea where the follicle has burst, the very broad, yellowish white layer (Fig. 115, A, b), from which the body derives its name, is seen running around a red mass. It is this layer which, in a puerperal corpus luteum, is of very great breadth and has a rather reddish yellow tint; in a menstrual corpus luteum it is narrower, and very distinctly separated on the inner side from the freshly extravasated contents which

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Fig. 115. Formation of corpora lutea in the human ovary. A. Section of an ovary: a, a follicle recently burst and filled with coagulated blood (extravasation, thrombus), and around it the thin yellow layer; b, a follicle, which had burst at an earlier period, already corrugated, and provided with a diminished thrombus and thickened wall; c, d a still more advanced stage of retrogressive metamorphosis. B. External surface of the ovary, with the fresh rent caused by the bursting of the follicle, from the cavity of which the thrombus is seen peeping out. Natural size.

have filled up the follicle emptied by the extrusion of the ovule. This internal red mass consists entirely of thrombus, or blood-clot. The external layer essentially consists of fattily degenerated cells, and the yellow colour which it bears is occasioned by the refraction produced by the numerous minute particles of fat. This is not a real colour, but a phenomenon of interference.

A similar change you see in a lung which we took today out of the body of a man who, after caries of the internal ear, had a thrombosis of the transverse sinus with gangrenous metamorphosis, and, in consequence, gangrene of the lung. The cells we have here to deal with were not taken, however, from the actual seat of the gangrene itself, but from a condensed spot in the neighbourhood, where a very abundant accumulation of masses of proliferating epithelium (catarrhal pneumonia) had taken place. In this case you can see the difference between fat-granule-cells (Fig. 66), and other forms of granulecells, very prettily shown. For in these masses of epithelium which have filled up the alveoli of the lung, you find extremely numerous pigment-cells, such as in cases like this are brought up in great quantity in the sputa, which are indebted to them for the well-known smoky grey spots (Fig. 11, J). At first sight it is difficult to make a distinction between fat-granule-, and pigment-cells, inasmuch as in both cases apparently the same image is offered to our view. In the one case the cells appear as brownish yellow corpuscles, although their individual particles have no positive colour; in the other, on the contrary, they contain unquestionable, grey, brown, or black, pigment. The diagnosis of ordinary granule-cells, by which fat-granule-cells are always meant, is, however, very important, because in other parts also, as for example, in the brain, we find both sorts of granule-cells, those containing fat and those containing pigment, side by side; and even when the affection is limited to very small spots in

FATTY DEGENERATION OF RENAL EPITHELIUM. 347

this organ, it is very important1 for the interpretation of the objects found to know whether they belong to the one or the other class. For in the brain also the accumulation of a number of minute particles of fat may on the whole, through the multiplication of the refracting points, occasion an intense yellow colour. The different proportion of fat and the degree of its division produce a great number of varieties of colour which at last manifest themselves very distinctly to the naked eye, so that the more minute and the more closely aggregated the fatty particles are, the more marked is the production of a pure yellow or brownish-yellow hue even to the naked eye. What we call yellow softening of the brain is also really nothing more than a form of fatty degeneration, where the yellow appearance of the affected spot is owing to the accumulation of finely granular fat. As soon as this is removed, the colour also disappears, although the fat thus extracted is by no means of so deep a hue as the spot whence it was derived. The refraction of light between the extremely minute particles is the chief cause of this phenomenon of colour.

It is self-evident that at every point, where the fatty degeneration attains a high pitch, great opacity will always present itself. A transparent part becomes opaque when it undergoes fatty degeneration; this we see, for example, in the cornea, the fatty clouding of which may become so marked in arcus senilis, that an entirely opaque zone is thereby produced. Even in places, where the parts were originally not transparent, but only translucent, a complete opacity may be seen to declare itself in proportion as the process of fatty degeneration progresses.

Consider, for example, a kidney in the stage of fatty degeneration. I shew you here a preparation which does not present the ordinary granular atrophy of Bright's disease, but a more chronic and smooth form. The con

1 1'or the pigment would point to apoplexy, the fat to softening.

voluted uriniferous tubules of the cortex are very much enlarged, and the whole of its epithelium is in a state of fatty degeneration, so that within the tubules there is really nothing else to be seen than a densely crowded mass of fat-granules. If however microscopical sections are very carefully prepared, the fat-granules are in the first instance still seen collected in isolated groups (as granule-cells or granule-globules, Fig. 98); but upon slight pressure the mass disperses in such a way, that the whole uriniferous tubule is uniformly filled with finely emulsive contents. Even with the naked eye you can distinctly recognize the change; and as soon as one has once become accustomed to discriminate with some degree of accuracy between these less obvious conditions, there is not the slightest difficulty in discovering from the aspect of such a part the presence of a change in the renal epithelium, and that indeed of this particular kind, for there is no other form of change which could be compared to it. If you examine the surface of the kidney you will perceive that over the rather greyish, translucent ground, upon which the Stellulaa Verheynii1 stand out, small opaque spots are scattered in the most varied manner, most of them forming not real points, but usually small segments of an arc. These will always be found to be parts of the convolutions of uriniferous tubules which have mounted up to the surface. These yellowish, opaquelooking convolutions correspond to fattily degenerated uriniferous tubules, or to speak more accurately, to uriniferous tubules filled with fattily degenerated epithelium. If a section be compared with the surface, the same markings are very distinctly seen to run through the whole of the cortex, from the periphery down to the upper borders of the medullary cones, and to invest the individual cones formed by the tubuli recti which are prolonged into the cortical substance—at pretty regular intervals.

1 The stellate veins.- -thansl.

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