Avian and mammalian kidneys can produce a urine hyperosmotic to the blood by means of a renal countercurrent system. Birds are uricotelic; mammals are ureotelic. It is proposed that the inner medulla present in mammalian, but not in avian kidneys serves specifically to accumulate urea in the inner and outer medulla. Among mammalian kidneys the degree to which urea accumulates in the inner medul...

Hydronephrosis, "distension in varying degrees of pelvis and calyces, accompanied by progressive atrophy of renal parenchyma due to obstruction in urinary flow", is an apparently simple reno-urinary disease, but, in reality, by association of its own characters with those conferred by causative lesions, becomes of a significant complexity. The purpose of this paper is to demonstrate the pluriva...