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ELEMENTS OF MATERIA MEDICA.

the temperature of the fluid, since its mechanical effects are compara-tively slight. In the common vapour douche the temperature of theaqueous vapour does not exceed that employed in the vapour bathsalready described; and in such cases it may be regarded as a kind oflocal vapour bath. Thus in some affections of the ear, as otitis, otorrhcea,and otalgia, a stream of aqueous vapour may be applied to the meatusauditorius extemus with great benefit; and the most ready means ofeffecting this is by a funnel inverted over a vessel of hot water, the earbeing placed over the orifice of the funnel.

Sometimes steam has been used—that is, aqueous vapour heated to212° F.; and, of course, it acts as a caustic if sufficiently long applied,causing sometimes an extensive and deep eschar. In this respect itsaction is similar to that of boiling water, from which, indeed, it princi-pally differs in the circumstance of having a much larger quantity ofspecific heat, and in the great facility with which we can localize itseffects. It may be readily applied to any part of the body by means of asmall boiler (copper or tin), furnished with a pipe and stop-cock, andheated by a spirit lamp. It has been used as a powerful counter-irritantin diseases of the hip-joint, neuralgic pains, chronic rheumatism, &c.;but the objections to its use are the great pain and the danger of itsemployment; for it is a more painful application than many other modesof causing counter-irritation, while its effects arc inconstant.

The action of the liquid douche depends in a great measure on thetemperature of the liquid, but in part also on the mechanical action ofthe water. This effect of percussion is common to both the cold and hotdouche, and by continuance excites pain and inflammation of the part.Tins local excitement is observed almost immediately when hot water isemployed, but takes place more slowly when we use cold water ; indeed,the long action of a stream of cold water may act as a sedative, andcause all the effects which I have already described as the primaryeffects of cold applications.

The effect of the douche is, however, not altogether local, since theneighbouring parts, and even the whole animal economy, soon becomeaffected. A column of water twelve feet high, made to fall perpendicu-larly on the top of the head, excites such a painful sensation, that, we aretold, the most furious maniacs who have once tried it may sometimes beawed merely by the threat of its application ; and hence one of its usesin madness, as a means of controlling the unfortunate patient.

The cold douche is applicable to those cases of local disease requiringa powerful stimulus. For example, chronic affections of the joints, oflong standing, whether rheumatic, gouty, or otherwise, paralytic affec-tions of the limbs, old glandular swellings, and those forms of insanity inwhich there are no marks of determination of blood to the head. Thewarm douche may be employed in similar cases.

For a variety of local purposes, a syringe is employed to throw a jet ofwater on particular parts, as into sinuous ulcers, or into the vagina, intothe ear, into the rectum, &c., constituting thus a kind of douche.

Local uses. — Hot, warm, and cold water, applied to particular partsof the body, may be regarded as local baths. Cold water is applied toproduce evaporation, and thereby to generate cold, with the view ofrelieving local irritation and inflammation. In ophthalmia, phrenitis,and even in gout (though in the latter complaint the practice has been