One of the tribulations of the student of medicine during his progress toward the goal of the doctorate lies in the necessity of considering the various theories, often seemingly contradictory or at least conflicting, that different teachers present in explanation of some of the fundamental phenomena with which he must deal. This debate of preferences has long been characteristic of discussions of kidney function. The unique structural and circulatory mechanisms in the renal tissues have stimulated interest and occasioned experiments that sometimes seem to lead to irreconcilable conclusions. Hence, one hears of the "filtration hypothesis," the "secretory theory," the problem of reabsorption, the relative participation of glomerulus and tubule in the elaboration of urine, the preponderance of pressure changes over velocity or volume of blood flow in the renal vessels or vice versa.
The true significance of the problem has been expressed well by Richards.4 The question, he remarks,
RÔLE OF THE GLOMERULI IN RENAL FUNCTION TESTS WITH DYES. JAMA. 1924;83(2):122–123. doi:10.1001/jama.1924.02660020044021