This paper treats of the physical influences which promote the secretion of urine, as far as can be demonstrated by experiments upon animal membranes and the kidneys of animals recently killed. Before going on to consider the subject I may be permitted simply to mention the theory held regarding the means by which the kidney performs its function, and also say a word or two in connection with the structure of that organ. As regards its histology the kidney may be said to be composed of two elements—(1) the blood-vessels, and (2) the tubuli uriniferi. (This is leaving out of account the lymphatic arrangement.) The kidney receives its supply of blood from the renal artery, which, as it passes into the substance of the kidney, penetrates the cortical portion and gives off branches.