=Pyelitis.= Inflammation of the walls of the sinus of the kidney, is thus designated. It may exist alone, or in company with inflammation of the kidney, constituting _Pyelonephritis_. It appears to originate, in many cases at least, secondarily to an attack of cystitis, and would seem metastatic in its nature, the ureter connecting the two inflamed organs, escaping the disease. It is a very serious, and often rapidly fatal disease. Where the inflammation extends to the kidney tissue, suppuration is likely to follow, resulting thus in the formation of an abscess. =Abscesses.= Renal abscesses are found bordered by a red injected halo, which gives rise to a friable product, thus leading to an extension of the abscess. The mucous membrane of the calices and the pelvis, especially when a calculus is present, is softened and inflamed, and secretes a purulent fluid. The process of suppuration may continue until the whole organ is converted into a pouch of pus. Then, or even before the organ is quite destroyed, the abscess may make its way by the usual process of absorption, and discharge its contents into the calices, to be carried off by the urinary passages; into the ascending or descending colon, or the duodenum, to be passed with the fæcal evacuations; or, after perforating the diaphragm, into the bronchi, whence they are removed by coughing; or through the lumbar muscles; or it may burst into the peritoneal cavity and cause rapid death. This disease rarely attacks more than one kidney, and the other healthy kidney generally enlarges and becomes capable of performing a double amount of work. It is well to remember, that a mass of softened fibrinous exudation, bordered by a red halo, may sometimes so far simulate an abscess, that only the microscope can distinguish the one from the other. =Inflammation of the Capsule= may take place and cause fibroid thickening, more or less induration, atrophy, and obliteration of the organ. The cortical substance generally suffers most, and the surface is sometimes overspread with purulent matter, while the tissue itself becomes sloughy or gangrenous, or is only congested and softened. =Morbus Brightii.= _Bright’s Disease._ _Degenerative disease of the kidneys._ _Desquamative and un-desquamative nephritis._ In view of the impossibility of accurately defining the term _Bright’s Disease_, we will describe it in general as including those diseases of the kidneys which, in some stage or other of their course, are accompanied by albuminuria, or dropsy, or both. And as it would be foreign to the object of this work, to enter into an examination of the respective merits of the theories, in reference to the nature and course of this disease, we will adopt that classification which seems best adapted to our purpose, and proceed to consider the morbid anatomy of Bright’s Disease in its various forms and stages as first suggested by Virchow in his Cellular Pathology, and adopted and developed by Stewart.[31]