The classification of nephritis is a source of great confusion to students and practitioners of medicine. Most discussions of this subject take the form of a defense of some proposed classification. It has seemed to me that a simpler approach would be a statement and discussion of the problems involved rather than the presentation of some particular classification. This method should furnish a means by which any rational classification may be made intelligible.
There are many reasons why a satisfactory classification of nephritis is difficult to attain. In the first place, the kidneys are highly complex organs. This complexity becomes evident from a mere cataloguing of the various parts of the kidney more or less intimately associated with its function: the renal arteries and arterioles, including the afferent vessels; the glomeruli with their tufts of capillaries lined with endothelium and covered with flat epithelium; Bowman's capsule; the tubules with their