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.

The circulation may also be lessened by such drugs as aconite, antimony, and ipecacuanha.