Syn. Refrigerants.

These are medicines which reduce the force of the circulation by an immediate influence, independently of any depletion they may occasion, and without any obvious direct action on the nervous system of animal life. Whatever effects they may produce upon the brain, considered as the centre of the animal functions, are probably the result of their primary action upon the great organic functions, especially those of circulation and respiration.

It does not follow, from the possession of this depressing power over the circulation, that they are also sedative in their local operation. On the contrary, some of them are energetic local irritants, as the preparations of antimony, for example; and most of them conjoin with their. general sedative property that of stimulating one or more of the secretions.

Their influence on the circulation is exhibited in a diminution of the force, fulness, and frequency of the pulse, and of the temperature of the body. From the latter effect, they are frequently denominated refrigerants. Under certain circumstances, some of them produce coolness by a direct chemical influence; as when nitre is swallowed in the state of powder, and renders latent a portion of the free heat of the stomach in the act of solution; but generally their refrigerant effect is probably dependent exclusively on the diminished energy of the circulation, and the consequently smaller amount of change in the blood that takes place in the pulmonary and systemic capillaries.

The respiration is depressed correspondingly with the circulation, and probably as a consequence of the diminished amount of blood sent through the lungs.

How far the directly depressing effects of these medicines might be carried by an increase of the quantity taken, it is not easy to determine; as, by their evacuant and locally stimulant properties, the more energetic of them superadd an exhausting depletion, and a violent inflammatory or irritant effect in the part to which they may be applied, to their immediate sedative influence; but, whether from their depressing effects alone, or from these conjoined with the local results referred to, many of them are capable of destroying life.

When continued long, in regular medicinal doses, they act injuriously on the health by enfeebling all the functions, through the diminished supply of blood. indigestion, anaemia, emaciation, and general debility result; and, though it might be difficult to adduce instances in which they have directly produced death in this way, yet there can be no doubt that they may operate fatally by incapacitating the system for resisting ordinary diseases.

The arterial sedatives are applicable to the treatment of all diseases in which there is an excess of arterial excitement, and at the same time a sthenic state of the system. Hence they are much used in inflammation, high vascular irritation, and fever of vigorous action. They may often too be employed to diminish febrile heat and vascular excitement, even when the vital forces are enfeebled and the blood impaired, as in typhoid diseases; but, under these circumstances, more caution should be used, and those medicines of the class should be selected which are least depressing, and have least tendency to impair the blood. Thus, the vegetable acids, as the citric in the form of lemon-juice, and the neutral alkaline salts, as citrate of potassa in the form of neutral mixture or effervescing draught, may be given when the antimonials might be contra-indicated.