In every patient suffering from chronic diffuse nephritis there are a number of symptoms which seem to depend directly upon other conditions, and not upon the kidney lesions; for if these conditions are removed the symptoms disappear, although the kidney lesions continue. To this category of symptoms seem to belong the headache, delirium, stupor, coma, and convulsions, the nervous dyspnoea, the vomiting in part, the dropsy in part, the diminution of urine in part. All these symptoms are due to disturbances of the circulation, and the disturbances of the circulation are produced by a number of causes which may act separately or together. Changes in the valves and walls of the heart, in the force and regularity of the heart's contraction, in the walls and size of the arteries and capillaries, and in the volume and composition of the {96} blood, each, separately or associated, may interfere with the proper circulation of the blood, and this interference usually takes the form of too much blood in the veins and too little blood in the arteries. Anatomical changes in the valves of the heart, in its walls, and in the walls of the arteries and capillaries cannot be influenced by any means at our command. The force and regularity of the contractions of the heart can, however, be very decidedly modified by drugs. Opium in moderate doses makes the heart's action slower and stronger; iodide of potassium makes the heart's action more regular; convallaria makes the heart's action slower and stronger; digitalis increases the force of the heart's action, but at the same time contracts the arterioles; aconite and veratrum viride make the heart's action slower and more feeble. The size of the arteries and capillaries can also be altered by drugs. Nitrite of amyl and nitro-glycerin relax and dilate the whole arterial and capillary system; chloral hydrate dilates the arterioles (Fothergill). The volume of the blood can be diminished by bloodletting and by eliminating the plasma of the blood indirectly by sweating, purging, or diuresis. The symptoms which can be ascribed directly to the presence of the kidney disease are--(1) The changes in the composition of the blood. We have still very little exact knowledge of what these changes are, but we may say generally that there is an increase in the relative quantity of the watery constituents of the blood and of the excrementitious products which should be eliminated by the kidneys. (2) The changes in the quantity of urine probably depend partly on the changes in the circulation, partly on the composition of the blood, and partly upon the structural changes in the kidneys. The albumen and casts seem to be directly due to the kidney lesion. (3) The changes in the nutrition of the patient, the disturbances of digestion, and some of the headaches, all seem to belong directly to the kidney disease. Now let us try to apply these principles to the practical treatment of the different symptoms.