LESIONS.--The connective tissue behind the kidney seems to be the usual point of origin of the inflammatory process, and it is here that the pus first collects. After the abscess has reached a certain size the suppuration seems to have a natural tendency to spread and the pus burrows in different directions--backward through the muscles; downward along the iliac fossa, even as far as the perineum and scrotum or vagina; forward into the peritoneal cavity, the colon, or the bladder; upward through the diaphragm. The kidney is either compressed by the abscess or its tissue also becomes involved in the suppurative process. The soft parts around the abscess become thickened. ETIOLOGY.--Perinephritis is either secondary or primary. The secondary cases are due to extension of the inflammation from abscesses in the vicinity, such as are formed with caries of the spine, pelvic cellulitis, puerperal parametritis, perityphlitis, suppuration of the kidneys, and pyelo-nephritis. The primary cases occur after exposure to cold, after contusions over the lumbar region, great muscular exertion, and without discoverable cause. The lesion is said to complicate typhus and typhoid fever and smallpox. The disease occurs both in children and adults, most of the cases reported having been between the ages of twenty and forty years. SYMPTOMS.--The disease begins regularly with pain and tenderness referred to the lumbar region on one side between the lower border of the ribs and the crest of the ilium, sometimes to a point above or below this. At about the same time are developed repeated rigors, a febrile movement with evening exacerbations, sweating, loss of appetite, vomiting, and prostration. These are all the symptoms for from one to two weeks. Then the skin over the lumbar region on one side becomes red and oedematous; the corresponding thigh is kept flexed and rigid, for any movement of it gives pain. Then the lumbar region becomes more and more swollen until fluctuation can be made out, and finally the abscess breaks through the skin. If such cases are left to run their course the abscess may reach a very large size. If the pus does not extend backward, but in some other direction, the symptoms are more obscure, for the local symptoms of an abscess in the back are absent. If the abscess ruptures into the peritoneal cavity, the symptoms of acute general peritonitis are suddenly developed. If it perforates into the colon or bladder, the pus is discharged with the feces or the urine. If the perforation is through the diaphragm, there will be empyema, or the lung becomes adherent and pus is coughed up from the bronchi. As soon as the abscess is opened and the pus escapes the acute constitutional symptoms subside. Trousseau believes that the inflammatory process sometimes stops short of the production of pus. In such cases of course there are no evidences of the formation of an abscess. The disease may terminate in different ways: {103}