These are substances which lessen the secretion of sweat: Acids.

Belladonna and Atropine.

Hyoscyamus.

Amanita muscaria and muscarine. Agaricus albus. Jaborandi and Pilocarpine.

Nux vomica and Strychnine.

Quinine.

Picrotoxine.

Ipecacuanha (compound powder). Zinc salts.

These remedies may act (1) on the sweat-glands themselves by lessening the excitability either of the secreting cells or of the secreting nerves; (2) on the sweat-centres, by lessening their excitability or removing the excitant; and (3) on the circulation. Belladonna in large doses paralyses the ends of the secreting nerves, just as it does in the salivary glands, so that the sweat-glands will not secrete even when a strong stimulation is applied to their nerves. As belladonna acts thus when locally applied, it may be used for local sweating in the form of extract or of solution of atropine painted on, or rubbed over, the surface. It is thus useful in cases of local sweating of the palms of the hands and soles of the feet. It may also be given internally to paralyse the ends of the secreting nerves, and thus to arrest the night-sweats in phthisis. But in all probability its beneficial effect in the night-sweats of phthisis is not dependent on its paralysing action on the secreting nerves, for it is useful in doses which appear too small to produce this effect, and which also do not act immediately, but rather after some time. Its utility in such cases, therefore, is probably due to an effect on the nerve-centres, and especially to a stimulating action on the respiratory centre.

The night-sweats of phthisis are usually followed by great weakness and prostration, which has sometimes been attributed to the loss of salts and organic matter contained in the sweat. But the quantity of these is very small, and the same depression is not noticed when there is an increase of two or three ounces in the daily secretion of urine, although it will carry off quite as large a quantity of both salts and organic matter. Nor is the same depression produced by the profuse sweating due to active exertion, nor even by the sweating in ague. The depression is not the consequence of the profuse sweat; both are probably the consequence of one common cause. This cause I believe to be partial failure of the respiration and consequent accumulation of carbonic acid in the system, which leads at the same time to stimulation of the sweat-centres and impairment of tissue-change throughout the body generally.

Fig. 153.   Diagram to illustrate the action of antihidrotics. The secretory nerves passing to the sweat glands from the sweat centres in the spinal cord have been represented as a single nerve for the sake of simplicity.

Fig. 153. - Diagram to illustrate the action of antihidrotics. The secretory nerves passing to the sweat-glands from the sweat-centres in the spinal cord have been represented as a single nerve for the sake of simplicity.

In healthy persons the respiratory centre is more sensitive to the stimulus of carbonic acid than other parts of the nervous system. Thus any increase in the venosity of the blood at once stimulates this centre, and through it the diaphragm and respiratory muscles of the thoracic wall, rendering the respiration more active, and increasing artefialisation. Consequently, the blood does not become venous enough to stimulate the sweat-centres. But when the respiratory centre is depressed by excessive reflex stimulation during the day in the process of coughing, and by the natural depression which occurs during sleep, it may respond less readily to the stimulus of venous blood. The amount of carbonic acid in the blood may thus accumulate to such an extent that the sweat-centres are stimulated before the respiratory centre responds, and thus the profuse sweats which are so depressing to the patient may occur.

It is probable that this is only part of the truth, and that there are other factors in the production of abnormally profuse sweats; for in children suffering from rickets, the head perspires profusely during sleep, yet the mucous membranes are of a bright rosy colour. Nevertheless, acting on this idea, I have given at night such substances as are powerful stimulants to the respiratory centre, like nux vomica and strychnine, and I have found that the sweating is usually arrested by them. A small dose is sometimes sufficient, but occasionally it must be steadily increased until as much as half a drachm of the tincture of nux vomica is given at once. The only disadvantage that I have noticed from this treatment is that the excitability of the respiratory centre sometimes persists during the day, and renders the cough more troublesome. 1 have tried to remedy this by combining strychnine with opium, and partially succeeded. If we now review the remedies used in the night-sweating of phthisis, we shall see that almost every one of them has a stimulant action on the respiratory centre. This is possessed in a marked degree by atropine and hyoscyamus. Ipecacuanha has this action also, and its combination with opium, in the form of Dover's powder, although it causes sweating in healthy persons, tends to restrain it in phthisical patients. Picrotoxine, salts of zinc, and pilocarpine, all stimulate the respiratory centre also, and we find that the last is useful in the night-sweats of phthisis, although we should expect from its physiological action that it would be injurious, stimulating, as it does, the terminations of the secreting nerves in the sweat-glands themselves. It is possible, however, that in addition to the stimulation of the sweat-centres by venous blood, the night-sweats of phthisis may be sometimes increased by the high temperature of the patient, and in such cases quinine, as Murrell has pointed out, is likely to be most serviceable.