Marcello Malpighi discovered the glomerulus that bears his name in the 17th century, but it was not until the middle of the 19th century, in 1842, that William Bowman in London published his studies of the histological structure of the glomerulus and proposed that urine formation begins with glomerular secretion. At nearly the same time in Marburg, Carl Ludwig, unaware of Bowman's findings, proposed that urine formation begins with glomerular filtration followed by tubule reabsorption. The controversy lasted 80 yr. Prominent investigators weighed in on both sides. Rudolph Heidenhain's findings in 1874 swung the pendulum toward Bowman's theory until Arthur Cushny published his book, "The Secretion of Urine," in 1917, in which he found the evidence insufficient to prove either theory. In 1921, a young physician, Joseph Wearn, began his postresidency training in the laboratory of Alfred N. Richards. He read Cushny's book and learned how to expose the glomerulus of a living frog. Richards proposed that Wearn use that experimental preparation to inject epinephrine into the glomerulus. Wearn proposed a different experiment: instead of using injection, collect fluid from the glomerulus and analyze it. Richards agreed, and the landmark results of that experiment, published in 1924, settled the controversy. The modern era of renal physiology was born.