It may be that the chief function of the loops of Henle is to oppose resistance to the passage of fluids, thus heading up the secretion, and favouring the osmosis of water into it from the blood of the glomerular capillaries. It is possible that the calibre of the slender descending limbs is influenced by external pressure, their partial occlusion being increased, and the pressure in them raised, when the organ is very active and its intermediate zone turgid with blood. Various drugs influence the secretion of the kidney. In some cases their action seems to be mainly hydrostatic. They change the rate of flow by altering blood-pressure. Digitalis increases the force of the heart. The heart beating more strongly, blood-pressure rises. Higher blood-pressure is accompanied by a more copious secretion. This action of digitalis is far more marked when the heart is out of order than when it is healthy. In heart-disease the blood-pressure is unduly low, and the tissues become water-logged in consequence. When the blood-pressure is restored and a brisker capillary circulation established, water and waste products, which have accumulated in lymph, pass, as they ought to do, into the veins. Carried into the general circulation, they overflow from the kidney. It is a little difficult to realize the abundance of the body-fluids. From one-quarter to one-third of the whole body-weight is due to lymph, using this term in its most general sense. The waste products of tissues collect in the lymph. The blood circulating through capillary vessels which traverse lymph-spaces takes up water and waste products. Its just composition is maintained by the eliminating activity of the kidneys.