SEDATIVES are agents which produce a direct depression of the action of the vascular system, with little sensible evacuation. They differ from narcotics, inasmuch as their depressing effects arc not pre ceded by any obvious excitement or increased action of the heart and arteries. Whether they act primarily on the heart itself, or secondarily by a previous influence on the nervous system, is not clearly ascer tained. Some, such as the infusion of tobacco, and hydrocyanic acid, appear to destroy completely the sensibility of the heart, eo that it no longer responds to the stimulus of the blood ; but how this effect results is altogether unknown. Oxalic acid, when the dose is large, seems also to paralyse the heart; while iu less quantities it operates differently. [OxAtro Amu.] The peculiar mode of action of the articles entitled to be considered as pure sedatives has been detailed under the respective heads of DIGITALIS, HYDROCYANIC ACID, NICO TIARA, &c., and need not be repeated here. The medical employment of these formidable agents should never be had recourse to without competent authority and superintendence ; but as many cases of poisoning result from their accidental or criminal administration, it is needful to observe that the greatest promptness is requisite in the administration of appropriate remedies. Vital stimulants, such as
ammonia and brandy, are the beet ; and electricity or galvanism may be resorted to after the others.
Sulphuretted hydrogen, when breathed, injected into a vein of the rectum, or even applied to the skin, acts as a sedative, and in a email quantity can occasion death. It is largely disengaged from many decomposing substances, such as exist in stagnant pools, ditches, drains, and cesspools. Proximity to these produce effects more or lees serious according to the intensity of the gas. Even one of its com pounds, hydro-sulphuret of ammonia, is a potent sedative. Cold, when extreme, likewise acts as a sedative, Mit its mode of action has been already explained under BArnINO. Chloroform and other runes• thetics may be considered sedatives of the nerves of sensation.