All those described in the last section act on the cutaneous vessels, but in addition we have -

A. Diaphoretics, or drugs which increase the amount of perspiration. These may do so either by stimulating the sweat centres in the spinal cord, the nerves proceeding from the centres to the glands, the terminations of the nerves in the gland, or the glandular cells themselves; or dilatation of the cutaneous vessels may, by the increase in the amount of blood and the greater warmth, stimulate the glands and lead to an increase of sweat. It is difficult to tell whether drugs acting on the vessels do not also act on the other parts of the mechanism; and it is also difficult to decide whether a drug acts on the gland-cells or the termination of the nerves, so we will consider diaphoretics under two headings, those which act centrally and those which act peripherally. These are differentiated by observing whether the drug acts after the spinal cord is destroyed, or on a part of the skin after the nerves going to it are cut.

(a) Diaphoretics acting peripherally: Pilocarpine greatly increases the amount of sweat, acting in all probability on the nerve terminations in the gland-cells, but certainly not on the vessels. Nicotine also acts peripherally. Local applications of warmth, and alcohol taken internally perhaps act in the same way in addition to their vascular action.

(b) Diaphoretics acting centrally:

(1) Antimony salts.

(2) Ammonium acetate.

(3) Ammonium citrate.

(4) Ipecacuanha.

(5) Opium.

(6) Camphor.

(c) Diaphoretics whose mode of action is doubtful: Senega, cubeb, col-chicum, salicin, lobelia, arnica, aconite, potassium citrate and acetate. All these, except the last two, are very feeble.

When a diaphoretic acts very powerfully it is called a Sudorific.

B. Anhidrotics, or Antihidrotics, drugs which diminish the amount of perspiration. The part on which these act is determined in the same way as in the case of diaphoretics.

(a) Anhidrotics acting peripherally: Atropine is very powerful; it acts on the terminations of the nerves in the glands; and hyoscyamus and stramonium probably act in the same way. The local application of cold has a similar action.

(b) Anhidrotics the mode of action of which is doubtful:

(1) Acids.

(2) Muscarine.

(3) Nux vomica.

(4) Quinine.

(5) Picrotoxin.

(6) Zinc salts.

(7) Salicylic acid. (8) Camphoric acid.

Therapeutics

Diaphoretics are used for three purposes: either to increase the amount of sweat because that of the urine is failing, and for this purpose pilocarpine is largely used; or in the hope that poisons may be excreted by the sweat, hence the use of pilocarpine in uraemia; or as mild antipyretics, in order to increase the loss of heat by increased evaporation; for this purpose alcohol, ipecacuanha, ammonium acetate, and opium were formerly much employed, but of late years much more efficient antipyretics have been discovered.

Anhidrotics are used either for general conditions, as phthisis, or for local conditions, as sweating of the feet; but they are not of great use in medicine.

We do not know of any drugs which will alter the composition of the sweat, except in so far as that certain drugs may be excreted in the sweat when taken internally; such are iodine, potassium iodide, succinic, tartaric, and benzoic acids, the last in the form of hippuric acid.

We have no knowledge of the effects of drugs on the sebaceous secretion.

Certain drugs, when taken internally in large doses, produce a rash on the skin, possibly because in the course of their excretion through the skin they irritate it. Such are -

(1) Copaiba. (2) Cubeb.

(3) Bromides.

(4) Iodides.

(5) Turpentine.

(6) Belladonna.

(7) Chioral hydrate.

(8) Opium.

(9) Quinine.

(10) Salicylic acid.

(11) Arsenical Salts.

(12) Acetanilid.

(13) Antipyrin.

(14) Phenacetin.

(15) Chloralamide.

(16) Antitoxins.

(17) Serums.

(18) Silver salts may discolor the skin.

(19) Sulphonal.

The following quite rarely produce an eruption:

(1) Iron.

(2) Strychnine.

(3) Creosoce.

(4) Mercury.

(5) Veratrum.

(6) Digitalis.

(7) Sulphur.

(8) Antimony. 9 Santonin.

(10) Cod Liver Oil.