Enough has already been said to show that all remedies which act as stimulants or tonics to the heart will strengthen the circulation of blood through the lungs. The symptom which most clearly points to the use of a lung or heart stimulant is a blue or purplish colour of the visible membranes, particularly the schneiderian.
In the acute stage of congestion of the lungs, when an indifferently-conditioned hunter is overtaxed, this blueness is very marked, and a judicious stimulant from the rider's flask may avert a dangerous illness. Ammonia, either given as a draught in water or inhaled, is one of the most effectual lung stimulants. The drugs elsewhere described as carminative have a quickening effect upon the circulation of blood in the lungs, and the stream appears to flow more freely as a result of such agents as unload the liver and bowels; very marked improvement often follows the administration of small doses of aloes and calomel, which in some indirect way have been proved by trainers to increase the respiratory power of the animals entrusted to them.
Expectorants may act, as previously suggested, by increasing the power of secretion and quantity of mucus, by loosening the too tenacious and insufficiently fluid matter, or by adding mechanical force to expel the accumulated material. There are coughs in which the animal is " too sore to cough"; a great desire exists, but the animal dares not yield to it because of the greater pain resulting. An expectorant which alters the character of the spit may make it possible, with much less effort, to get rid of the cause of irritation. In the treatment of horses we are somewhat restricted; we may not give an emetic, which is found in the dog to expel mechanically accumulated material in the bronchi. The relief thus obtained in so-called "stomach" coughs does not necessarily point to that viscus as the seat of disease, but rather gives proof of mechanical assistance afforded in the pressure forward of bronchial mucus, when, by the act of vomition the diaphragm is pressed against the lungs. While, as we have already indicated, expectorants act in a variety of ways, it may be said that their chief and most general action is to stimulate the circulation of the blood in the lining membranes of the air-tubes and produce an increased secretion. Inhaling the vapour of hot water is one of the most simple and effective means of producing this desirable action, and medicaments of various kinds are frequently added. Of these may be mentioned the balsams of Peru and Tolu, copaiba and storax, camphor, myrrh, benzoin, and other volatile drugs, while for certain specific diseases agents are prescribed for inhalation for their antiseptic and other qualities rather than as pure stimulants or expectorants. Among this class, carbolic acid, turpentine, tar, eucalyptus, and other essential oils play an important part in the treatment of disease. Special apparatus is now made for giving inhalations, but in its absence the nose-bag may be made to do duty, with some hot bran and scalded hay, care, however, being taken not to scald the muzzle of the patient, as too frequently happens.