There are four well established types of renal disease that must be considered in a discussion of nephritis. A brief explanation of each of these will be given in order to establish the limitations of the group under discussion.
Pyelonephritis.—This is an acute or chronic exudative inflammation distributed in patches throughout the kidneys, and extending from the cortex throughout the pyramids into the pelvis. It is caused by bacteria, usually staphylococci or colon bacilli. In most instances the bacteria are carried to the kidney by the blood; but in cases of obstruction of the lower urinary tract they may enter from the urine. In the earlier stages of a hematogenous infection, before there has been extension to the pelvis, the lesions are spoken of as abscesses. Extension of the infection to the capsule may produce perinephritis or perirenal abscess. Infection of a dilated pelvis causes pyonephrosis. The disease is frequently