Around the turn of the 20th century, Ernest Henry Starling (1866-1927) made many fundamental contributions to the understanding of human physiology. With a deep interest in how fluid balance is regulated, he naturally turned to explore the intricacies of kidney function. Early in his career he focused upon the process of glomerular filtration and was able to substantiate the view of Carl Ludwig that this process can be explained entirely upon the basis of hydrostatic and oncotic pressure gradients across the glomerular capillary wall and that the process can be regulated by alterations in the tone of the afferent and efferent arterioles. To explore renal tubular function he employed a heart-lung-kidney model in the dog and was able to infer that certain substances are reabsorbed by the tubules (e.g. sodium chloride) and certain by tubular secretion (e.g. uric acid, indigo carmine dye). By temporarily blocking tubular function using hydrocyanic acid he was able to conclude that secreted substances must be taken up on the peritubular side of the cell and concentrated within the cell to drive the secretory process. Finally, he was able to appreciate that the kidney is an organ which is regulated according to the needs of the organism and that the processes of glomerular filtration, tubular secretion and reabsorption are all subject to regulatory influences, which have evolved to conserve the normal chemical composition of the cells and fluids of the body.