On placing thin sections of the kidney under the microscope, some of the tubes are seen to be in precisely the same condition as in a case of acute desquamative nephritis : they are filled and rendered opaque by an accumulation within them of nucleated cells, differing in no essential respect from the normal epithelium of the kidney. This increase in the number, and this slight alteration in the character of the epithelial cells are the result of the elimination by the kidney of mal-assi inflated products, which are being continually developed in gouty and intemperate subjects, and which are not normal constituents of the renal secretion.
There would evidently be a certain limit to the number of cells which can be formed in any one of the uriniferous tubes ; for although some of the cells escape with the liquid part of the secretion, and so may be seen in the urine, as in a case of acute desquamative nephritis, yet in many of the tubes the cells become so closely packed that the further formation of cells becomes hnpossible, and the process of cell-formation, and consequently of secretion within these tubes, is arrested. The cells, thus formed and filling up the tube, gradually decay and becomes more or less disintegrated. While these changes are occurring in the tubes, the Malpighian bodies frequently continue quite healthy, their capsules for the most part transparent, and the vessels in their interior perfect. From these vessels water, with some albumen and coagulable matter, is continually being poured into the tubes ; and, as a conse quence of this, the disintegrated epithelial cells are washed out by the current of liquid flowing through the tubes, so that, on ex amining the sedimentary portion of the urine, we find in it cylindrical moulds of the urinary tubes, composed of epithelium in different degrees of disintegration, and rendered co herent by the fibrinous matter which coagu lates amongst its particles. (fig. 170.) There is reason to believe that when the pro cess of cell-developnnent and of secretion have once been arrested by a tube becoming filled with its accumulated contents, the tube never recovers its lining of normal epithelial cells ; but when the disintegrated epithelium has been washed away from the interior of the tube, the basement membrane may be seen in some cases entirely denuded of epithelium ; in other tubes a few granular particles of the old and decayed epithelium remain (fig. 171.) ; and again, in other instances, the interior of a tube which has been deprived of its proper glandular epithelium is seen' lined by small delicate transparent nucleated cells (fig. 172.),
very similar to those which may sometimes be seen covering the vessels of the Malpighian tuft. (rule ant“g. 160.) After the tubes have lost their normal epithelial lining they may undergo one of the three following changes. 1. In some in stances a peculiar whitish glistening material is thrown into the tubes, some of which escapes with the urine in the form of cylin drical moulds of the tubes, the appearance of which as seen in the urine is somewhat im perfectly represented infig. 173. The effect tubes form the serous cysts which are so commonly seen in the cortical portion of the kidney. And it is remarkable that the moni liforrn appearance of the dilated tubes, as seen in the microscopic specimens, is in many instances preserved even when the tube is so much dilated as to form cysts visible to the naked eye. (Fig. 174.) of this material being effused into the tubes appears to be to obliterate them, and in some instances it apparently becomes organised into fibrous tissue.
2. Another change which the tubes un dergo in consequence of losing their epithelial lining, is that of becoming atrophied. The power of separating the solid urinary consti tuents from the blood resides in the epithelial cells which line the convoluted tubes. After the destruction of the cells the secreting power is lost, and as the normal action of the cells is certainly one of the essential conditions for maintaining the continued flow of blood to the tubes, so the removal of the cells is very commonly followed by a diminished afflux of blood, and a consequent wasting of the tubes.
3. Another change consequent upon the destruction of the epithelial cells is, in a cer tain sense, the reverse of the preceding. The tubes appear to retain the power of secreting serum, which fills and dilates the tube in con sequence of its escape being prevented by epithelial debris choking up the lower ex tremity of the tube. When once a tube is brought into this condition the process of dilatation may proceed to an almost unlimited extent. The tube bulges in the intervals of the fibrous matrix, and assumes the appear ance represented in fig. 172c. These dilated Mr. Simon, in a paper on " Subacute In flammation of the Kidney,"* has propounded the theory that these cysts are greatly dilated epithelial germs, which become thus mon strously developed in consequence of the destruction of the basement membrane of the tubes.