Aloes stimulate the r.e.c.t.u.m internally mixed with the circulating blood; and sea-salt by injection externally. Now as the capillaries, which secrete the perspirable matter, lie near the surface of the body, the application of external heat acts immediately on their excretory ducts, and promotes perspiration; internally those drugs which possess a fragrant essential oil, or spiritus rector, produce this effect, as the aromatic vegetables, of which the number is very great.

4. It must be remembered, that a due quant.i.ty of some aqueous vehicle must be given to support this evacuation; otherwise a burning heat without much visible sweat must be the consequence. When the skin acquires a degree of heat much above 108, as appears by Dr. Alexander's experiments, no visible sweat is produced; which is owing to the great heat of the skin evaporating it as hastily, as it is secreted; and, where the sweat is secreted in abundance, its evaporation cannot carry off the exuberant heat, like the vapour of boiling water; because a great part of it is wiped off, or absorbed by the bed-clothes; or the air about the patient is not changed sufficiently often, as it becomes saturated with the perspirable matter.

And hence it is probable, that the waste of perspirable matter is as great, or greater, when the skin is hot and dry, as when it stands in drops on the skin; as appears from the inextinguishable thirst.

Hence Dr. Alexander found, that when the heat of the body was greater than 108, nothing produced sweats but repeated draughts of cold water; and of warm fluids, when the heat was much below that degree. And that cold water which procured sweats instantaneously when the heat was above 108, stopped them as certainly when it was below that heat; and that flannels, wrung out of warm water and wrapped round the legs and thighs, were then most certainly productive of sweats.

5. The diaph.o.r.etics are all said to succeed much better, if given early in the morning, about an hour before sun-rise, than at any other time; which is owing to the great excitability of every part of the system after the sensorial power has been acc.u.mulated during sleep. In those, who have hectic fever, or the febricula, or nocturnal fever of debility, the morning sweats are owing to the decline of the fever-fit, as explained in Sect.

x.x.xII. 9. In some of these patients the sweat does not occur till they awake; because then the system is still more excitable than during sleep, because the a.s.sistance of the voluntary power in respiration facilitates the general circulation. See Cla.s.s I. 2. 1. 3.

6. It must be observed, that the skin is very dry and hard to the touch, where the absorbents, which open on its surface, do not act; as in some dropsies, and other diseases attended with great thirst. This dryness, and shrivelled appearance, and roughness, are owing to the mouths of the absorbents being empty of their accustomed fluid, and is distinguishable from the dryness of the skin above mentioned in the hot fits of fever, by its not being attended with heat.

As the heat of the skin in the usual temperature of the air always evinces an increased perspiration, whether visible or not, the heat being produced along with the increase of secretion; it follows, that a defect of perspiration can only exist, when the skin is cold.

7. Volatile alcali is a very powerful diaph.o.r.etic, and particularly if exhibited in wine-whey; 20 drops of spirit of hartshorn every half hour in half a pint of wine-whey, if the patient be kept in a moderately warm bed, will in a few hours elicit most profuse sweats.

Neutral salts promote invisible perspiration, when the skin is not warmed much externally, as is evinced from the great thirst, which succeeds a meal of salt provisions, as of red herrings. When these are sufficiently diluted with water, and the skin kept warm, copious sweats without inflaming the habit, are the consequence. Half an ounce of vinegar saturated with volatile alcali, taken every hour or two hours, well answers this purpose; and is preferable perhaps in general to all others, where sweating is advantageous. Boerhaave mentions one cured of a fever by eating red-herrings or anchovies, which, with repeated draughts of warm water or tea, would I suppose produce copious perspiration.

Antimonial preparations have also been of late much used with great advantage as diaph.o.r.etics. For the history and use of these preparations I shall refer the reader to the late writers on the Materia Medica, only observing that the stomach becomes so soon habituated to its stimulus, that the second dose may be considerably increased, if the first had no operation.

Where it is advisable to procure copious sweats, the emetics, as ipecacuanha, joined with opiates, as in Dover's powder, produce this effect with greater certainty than the above.

8. We must not dismiss this subject without observing, that perspiration is designed to keep the skin flexile, as the tears are intended to clean and lubricate the eye; and that neither of these fluids can be considered as excretions in their natural state, but as secretions. See Cla.s.s I. 1. 2. 3.

And that therefore the princ.i.p.al use of diaph.o.r.etic medicines is to warm the skin, and thence in consequence to produce the natural degree of insensible perspiration in languid habits.

9. When the skin of the extremities is cold, which is always a sign of present debility, the digestion becomes frequently impaired by a.s.sociation, and cardialgia or heartburn is induced from the vinous or acetous fermentation of the aliment. In this disease diaph.o.r.etics, which have been called cordials, by their action on the stomach restore its exertion, and that of the cutaneous capillaries by their a.s.sociation with it, and the skin becomes warm, and the digestion more vigorous.

10. But a blister acts with more permanent and certain effect by stimulating a part of the skin, and thence affecting the whole of it, and of the stomach by a.s.sociation, and thence removes the most obstinate heartburns and vomitings. From this the princ.i.p.al use of blisters is understood, which is to invigorate the exertions of the arterial and lymphatic vessels of the skin, producing an increase of insensible perspiration, and of cutaneous absorption; and to increase the action of the stomach, and the consequent power of digestion; and thence by sympathy to excite all the other irritative motions: hence they relieve pains of the cold kind, which originate from defect of motion; not from their introducing a greater pain, as some have imagined, but by stimulating the torpid vessels into their usual action; and thence increasing the action and consequent warmth of the whole skin, and of all the parts which are a.s.sociated with it.

II. 1. _Sialagogues._ The preparations of mercury consist of a solution or corrosion of that metal by some acid; and, when the dose is known, it is probable that they are all equally efficacious. As their princ.i.p.al use is in the cure of the venereal disease, they will be mentioned in the catalogue amongst the sorbentia. Where salivation is intended, it is much forwarded by a warm room and warm clothes; and prevented by exposing the patient to his usual habits of cool air and dress, as the mercury is then more liable to go off by the bowels.

2. Any acrid drug, as pyrethrum, held in the mouth acts as a sialagogue externally by stimulating the excretory ducts of the salivary glands; and the siliqua hirsuta applied externally to the parotid gland, and even hard substances in the ear, are said to have the same effect. Mastich chewed in the mouth emulges the salivary glands.

3. The unwise custom of chewing and smoking tobacco for many hours in a day not only injures the salivary glands, producing dryness in the mouth when this drug is not used, but I suspect that it also produces schirrhus of the pancreas. The use of tobacco in this immoderate degree injures the power of digestion, by occasioning the patient to spit out that saliva, which he ought to swallow; and hence produces that flatulency, which the vulgar unfortunately take it to prevent. The mucus, which is brought from the fauces by hawking, should be spit out, as well as that coughed up from the lungs; but that which comes spontaneously into the mouth from the salivary glands, should be swallowed mixed with our food or alone for the purposes of digestion. See Cla.s.s I. 2. 2. 7.

III. 1. Expectorants are supposed to increase the secretion of mucus in the branches of the windpipe, or to increase the perspiration of the lungs secreted at the terminations of the bronchial artery.

2. If any thing promotes expectoration toward the end of peripneumonies, when the inflammation is reduced by bleeding and gentle cathartics, small repeated blisters about the chest, with tepid aqueous and mucilaginous or oily liquids, are more advantageous than the medicines generally enumerated under this head; the blisters by stimulating into action the vessels of the skin produce by a.s.sociation a greater activity of those of the mucous membrane, which lines the branches of the windpipe, and air-cells of the lungs; and thus after evacuation they promote the absorption of the mucus and consequent healing of the inflamed membrane, while the diluting liquids prevent this mucus from becoming too viscid for this purpose, or facilitate its expuition.

Blisters, one at a time, on the sides or back, or on the sternum, are also useful towards the end of peripneumonies, by preventing the evening access of cold fit, and thence preventing the hot fit by their stimulus on the skin; in the same manner as five drops of laudanum by its stimulus on the stomach. For the increased actions of the vessels of the skin or stomach excite a greater quant.i.ty of the sensorial power of a.s.sociation, and thus prevent the torpor of the other parts of the system; which, when patients are debilitated, is so liable to return in the evening.

3. Warm bathing is of great service towards the end of peripneumony to promote expectoration, especially in those children who drink too little aqueous fluids, as it gently increases the action of the pulmonary capillaries by their content with the cutaneous ones, and supplies the system with aqueous fluid, and thus dilutes the secreted mucus.

Some have recommended oil externally around the chest, as well as internally, to promote expectoration; and upon the nose, when its mucous membrane is inflamed, as in common catarrh.

IV. 1. Diuretics. If the skin be kept warm, most of these medicines promote sweat instead of urine; and if their dose is enlarged, most of them become cathartic. Hence the neutral salts are used in general for all these purposes. Those indeed, which are composed of the vegetable acid, are most generally used as sudorifics; those with the nitrous acid as diuretics; and those with the vitriolic acid as cathartics: while those united with the marine acid enter our common nutriment, as a more general stimulus. All these increase the acrimony of the urine, hence it is retained a less time in the bladder; and in consequence less of it is reabsorbed into the system, and the apparent quant.i.ty is greater, as more is evacuated from the bladder; but it is not certain from thence, that a greater quant.i.ty is secreted by the kidnies. Hence nitre, and other neutral salts, are erroneously given in the gonorrhoea; as they augment the pain of making water by their stimulus on the excoriated or inflamed urethra. They are also erroneously given in catarrhs or coughs, where the discharge is too thin and saline, as they increase the frequency of coughing.

2. Balsam of Copaiva is thought to promote urine more than the other native balsams; and common resin is said to act as a powerful diuretic in horses.

These are also much recommended in gleets, and in fluor albus, perhaps more than they deserve; they give a violet smell to the urine, and hence probably increase the secretion of it.

Calcined egg-sh.e.l.ls are said to promote urine, perhaps from the phosphoric acid they contain.

3. Cold air and cold water will increase the quant.i.ty of urine by decreasing the absorption from the bladder; and neutral and alcalious salts and cantharides by stimulating the neck of the bladder to discharge the urine as soon as secreted; and alcohol as gin and rum at the beginning of intoxication, if the body be kept cool, occasion much urine by inverting the urinary lymphatics, and thence pouring a fluid into the bladder, which never pa.s.sed the kidnies. But it is probable, that those medicines, which give a scent to the urine as the balsams and resins, but particularly asparagus and garlic, are the only drugs, which truly increase the secretion of the kidnies. Alcohol however, used as above mentioned, and perhaps great doses of tincture of cantharides, may be considered as drastic diuretics, as they pour a fluid into the bladder by the retrograde action of the lymphatics, which are in great abundance spread about the neck of it. See Sect. XXIX. 3.

V. Mild cathartics. The ancients believed that some purges evacuated the bile, and hence were termed Cholagogues; others the lymph, and were termed Hydragogues; and that in most each cathartic selected a peculiar humour, which it discharged. The moderns have too hastily rejected this system; the subject well deserves further observation.

Calomel given in the dose from ten to twenty grains, so as to induce purging without the a.s.sistance of other drugs, appears to me to particularly increase the secretion of bile, and to evacuate it; aloe seems to increase the secretion of the intestinal mucus; and it is probable that the pancreas and spleen may be peculiarly stimulated into action by some other of this tribe of medicines; whilst others of them may simply stimulate the intestinal ca.n.a.l to evacuate its contents, as the bile of animals. It must be remarked, that all these cathartic medicines are supposed to be exhibited in their usual doses, otherwise they become drastic purges, and are treated of in the Cla.s.s of Invertentia.

VI. The mucus of the bladder is seen in the urine, when cantharides have been used, either internally or externally, in such doses as to induce the strangury. Spirit of turpentine is said to have the same effect. I have given above a dram of it twice a day floating on a gla.s.s of water in chronic lumbago without this effect, and the patient gradually recovered.

VII. Aloe given internally seems to act chiefly on the r.e.c.t.u.m and, spincter ani, producing tenesmus and piles. Externally in clysters or suppositories, common salt seems to act on that bowel with greater certainty. But where the thread-worm or ascarides exist, 60 or 100 grains of aloes reduced to powder and boiled in a pint of gruel, and used as a clyster twice a week for three months, has frequently destroyed them.

VIII. The external application of cantharides by stimulating the excretory ducts of the capillary glands produces a great secretion of subcutaneous mucus with pain and inflammation; which mucaginous fluid, not being able to permeate the cuticle, raises it up; a similar secretion and elevation of the cuticle is produced by actual fire; and by caustic materials, as by the application of the juice of the root of white briony, or bruised mustard-seed. Experiments are wanting to introduce some acrid application into practice instead of cantharides, which might not induce the strangury.

Mustard-seed alone is too acrid, and if it be suffered to lie on the skin many minutes is liable to produce a slough and consequent ulcer, and should therefore be mixed with flour when applied to cold extremities. Volatile alkali properly diluted might stimulate the skin without inducing strangury.

IX. The mild errhines are such as moderately stimulate the membrane of the nostrils, so as to increase the secretion of nasal mucus; as is seen in those, who are habituated to take snuff. The stronger errhines are mentioned in Art. V. 2. 3.

X. The secretion of tears is increased either by applying acrid substances to the eye; or acrid vapours, which stimulate the excretory duct of the lacrymal gland; or by applying them to the nostrils, and stimulating the excretory duct of the lacrymal sack, as treated of in the Section on Instinct.

Or the secretion of tears is increased by the a.s.sociation of the motions of the excretory duct of the lacrymal sack with ideas of tender pleasure, or of hopeless distress, as explained in Sect. XVI. 8. 2. and 3.

XI. The secretion of sensorial power in the brain is probably increased by opium or wine, because when taken in certain quant.i.ty an immediate increase of strength and activity succeeds for a time, with consequent debility if the quant.i.ty taken be so great as to intoxicate in the least degree. The necessity of perpetual respiration shews, that the oxygen of the atmosphere supplies the source of the spirit of animation; which is constantly expended, and is probably too fine to be long contained in the nerves after its production in the brain. Whence it is probable, that the respiration of oxygen gas mixed with common air may increase the secretion of sensorial power; as indeed would appear from its exhilarating effect on most patients.

III. CATALOGUE OF THE SECERNENTIA.

I. Diaph.o.r.etics.

1. Amomum zinziber, ginger. Caryophyllus aromaticus, cloves. Piper indic.u.m, pepper. Capsic.u.m. Cardamomum. Pimento, myrtus pimenta. Canella alba. Serpentaria virginiana, aristolochia serpentaria, guaiac.u.m.

Sa.s.safras, laurus sa.s.safras. Opium. Wine.

2. Essential oils of cinnamon, laurus cinnamomum. Nutmeg, myristica moschata. Cloves, caryophyllus aromaticus. Mint, mentha. Camphor, laurus camphora. Ether.

3. Volatile salts, as of ammoniac and of hartshorn. Sal cornu cervi.

4. Neutral salts, as those with vegetable acid; or with marine acid, as common salt. Halex. Red-herring, anchovy.

5. Preparations of antimony, as emetic tartar, antimonium tartarizatum, wine of antimony. James's powder.

6. External applications. Blisters. Warm bath. Warm air. Exercise.

Friction.

7. Cold water with subsequent warmth.

II. Sialagogues. Preparations of mercury, hydrargyrus. Pyrethrum, anthemis pyrethrum, tobacco, cloves, pepper, cowhage, stizolobium siliqua hirsuta.

Mastich, pistacia lentiscus.

III. Expectorants:

1. Squill, scilla maritima, garlic, leek, onion, allium, asafoetida, ferula asafoetida, gum ammoniac, benzoin, tar, pix liquida, balsam of Tolu.