Reduction of the volume of blood circulating in the lungs is the most certain means of reducing their irritability, and a determination of blood to a particular part is combated by remedies which create a diversion from what are commonly called vital centres to the skin or subcutaneous tissues; hence the use of poultices and fomentations, warm liniments, and still more active vesicants, as mustard. The internal application of heat to the air-passages is afforded by the inhalation of steam, and the effect is to cause dilatation of the air-passages, more particularly of those with which contact is most direct. The effect of saline and other aperients is also soothing to the lungs for the same reason that a diversion of blood to the bowels relieves the pressure in the respiratory system. Another means of soothing the air-passages and reducing circulation of blood in the lungs is rest from all muscular exertion. It is noticeable in horses how cough is excited by movement and allayed by repose.