A. Drugs acting on the Teeth. - Soaps and powders are used for cleaning the teeth. The basis of most tooth powders is chalk, which acts mechanically; charcoal is sometimes used in the same way. As the food is very liable to collect and decompose between the teeth, antiseptics, as quinine, borax and carbolic acid, are often mixed with tooth powders. Astringents such as krameria are employed if the gums are too vascular. Mineral acids and alum are injurious to the teeth if used for a long time, and iron is liable to stain them; therefore these substances are best taken through a glass tube, and should not be used as gargles for long periods.

Toothache may be relieved by local anodynes, as creosote, or pure carbolic acid. The tooth is plugged with absorbent cotton soaked in one of these. A piece of clean cotton must be placed over the carbolized cotton to prevent the carbolic acid from reaching the mouth. This method may damage the tooth-pulp.

B. Drugs acting on the Salivary Gland. - Much attention has been devoted to the submaxillary gland of the dog, and there is no reason for supposing that the other salivary glands of that animal or of other creatures, differ markedly from it. We know that the submaxillary gland is under the influence of the chorda tympani nerve, which contains vaso-dilator fibres, and also some which directly modify the secretion of the gland apart from the secondary effects, due to the alterations in the vessels, obtained when the chorda tympani is stimulated. This nerve has its centre in the medulla, and is capable of being excited re-flexly by stimulation of many nerves, even the sciatic, but especially by stimulation of the gastric branches of the vagus, and by the terminations in the tongue and mouth of the glossopharyngeal and gustatory nerves. The gland is also supplied with sympathetic branches which proceed from the cervical sympathetic trunk; these are vaso-constrictor, and can also modify the quality of the secretion; but we do not know so much about them as we do about the chorda tympani. Drugs which increase the amount of saliva have been called sia-logogues; those which decrease it, anti-sialogogues. It is clear that there are very many ways in which each of these might act, but here it will suffice to enumerate only those ways in which they are known to act.

1. Sialogogues acting either on the secretory cells or upon the terminations of the nerves in them. - Of these pilocarpus has been most studied, and by means of the experiments it has been proved to act either on the cells themselves or the terminations of the nerves in them. It acts equally well after section of all the nerves going to the gland. It acts when it is injected directly into the gland, but is prevented from reaching the general circulation. If it has been given, stimulation of the chorda or of the sympathetic produces no more effect on the amount of secretion than can be easily explained by the vascular effects.

Sialogogues falling under this heading are -

(1) Pilocarpus.

(2) Muscarine.

(3) Iodine compounds.

(4) Mercury.

(5) Nicotine.

(6) Physostigmine.

The last two probably act also by stimulating the centre in the medulla, for section of the chorda tympani decidedly lessens the secretion caused by them. Physostigmine soon ceases to cause an increase of the secretion, for it tightly contracts the vessels of the gland.

2. Sialogogues acting reflexly by stimulating the peripheral ends of afferent nerves. - Of these there are two important varieties:

(a) Those stimulating the gustatory and glosso-pharyngeal nerves in the mouth:

(1) All Acids and

(2) Acid Salts.

(3) Chloroform.

(4) Alcohol.

(5) Ether.

(6) All pungent substances, as mustard, ginger, etc.

(6) Those stimulating the vagus in the stomach:

Most emetics, especially Antimony and Ipecacuanha.

3. Anti-sialogogues acting either on the secreting cells or the terminations 0/ the nerves in them. - Of these atropine has been most studied, and it is proved to act directly on the gland by the fact that the administration of it prevents any increase of salivary secretion on stimulation of the chorda, although the vessels dilate as usual. It is highly probable that it acts upon the nerve terminations, because, even after considerable doses, quite paralyzing the secretion of chorda tympani saliva, stimulation of the sympathetic will still induce secretion.

Anti-sialogogues falling under this heading are -

(1) Belladonna.

(2) Hyoscyamus.

(3) Stramonium, and

(4) Nicotine in excess.

4. Anti-sialogogues acting reflexly by depressing the peripheral ends of afferent nerves. - Alkalies, opium, and any substances which allay irritation of the mouth. Part of the effect of opium is due to its depressing action on the medullary centre.

Therapeutics

A deficiency in the amount of saliva secreted is seen most markedly in fever, when the mouth becomes very dry, and the patient complains of thirst. Sometimes it is a disease in itself, and the origin of this malady is then probably nervous. It is a prominent symptom of belladonna poisoning. In fever, acid drinks, especially those containing carbon dioxide gas, lemonade, etc., are of use as sialogogues. Drinks which relieve this febrile thirst are called Refrigerants. For the condition known as "dry mouth" pilocarpus has been used, and it will relieve the dryness due to belladonna poisoning. Excessive salivary secretion is hardly met with except as a symptom of poisoning, especially by mercury, iodine or pilocarpus. In some forms of indigestion the saliva has a very unpleasant taste, and may even be diminished in quantity, but then the indication is to treat the indigestion.

C. Drugs acting on the Stomach. - Strictly speaking, we ought to consider these under the following heads: (a). Those drugs which, by modifying the secretion of hydrochloric acid or pepsin, influence the conversion of proteids into peptones and albumoses. (b). Those which influence the property possessed by the gastric juice of curdling milk. (c). Those which affect its antiseptic power by modifying the secretion of acid. (V). Those which modify the secretion of mucus. (e). Those which influence the nerves, the vessels, or the movements of the stomach. (/). Lastly, those which are emetics. Our knowledge, however, is not sufficient to enable us to do this, and the most useful classification is into those affecting the secretion of gastric juice as a whole, the secreted contents, the vessels, the nerves, the movements, and emetics.

1. Drugs increasing the amount of gastric juice secreted.- These are usually called Stomachics, and include a great many substances. Stimulants to the mouth reflexly increase the secretion of gastric juice; all bitter and aromatic substances act in this way, and they also increase the appetite. The mere presence of food in the stomach stimulates the gastric flow. Probably aromatics and bitters act also on the stomach itself.

The drugs which increase the flow of gastric juice are -

(1) Aromatics.

(2) Bitters.

(3J All alkalies (especially potassium and sodium bicarbon-ates, and Spiritus Ammoniae Aromaticus).

(4) Alcohol.

(5) Ether.

(6) Chloroform.

(7) Magnesia.

(8) Magnesium carbonate.

(9) Pungent substances (pepper, mustard, horse-radish).

Therapeutics

Stomachics are very largely used for the purpose of increasing the secretion of gastric juice in cases of dyspepsia.

2. Drugs decreasing the amount of gastric juice secreted.

(1) Mineral acids.

(2) Acetic acid.

(3) Many of those in the last list if given in large doses, e.g., alcohol, ether and chloroform.

Therapeutics

These drugs are never employed for this effect. It is particularly to be observed that while alkalies increase the secretion of the gastric juice, which is acid, they diminish that of the saliva, which is alkaline; but acids increase the secretion of the alkaline saliva, but diminish that of the acid gastric juice.

3. Drugs altering the composition of the gastric contents.- Acids and alkalies naturally modify the reaction of the gastric contents. For this purpose diluted mineral acids are often prescribed to be taken about two hours after a meal, in cases in which the cause of indigestion is thought to be that the amount of hydrochloric acid secreted is deficient. If the acid were given at meal-time it would prevent the secretion of the natural acid; but by giving it after the meal, when all the acid that the gastric juice is capable of forming has been secreted, the drug carries on the act of digestion. In case of indigestion in which, from the nature of vomited matters or from any other reason, it is considered that there is an excess of acid in the stomach, alkalies are given at meal-times, the favorite drug being sodium bicarbonate.

Pepsin is given, usually in combination with diluted hydrochloric acid, when it is probable that the cause of the indigestion is the secretion of too small an amount of pepsin; but in this, as in every other variety of dyspepsia, it is far more important to remove the cause of indigestion than to endeavor to modify the composition of the secreted gastric juice.

Many attempts have been made to try, by the administration of antiseptics, to prevent fermentation and putrefaction from going on in the stomach, but with a limited success, for a sufficient dose of any antiseptic may be frequently deleterious.

Here, even more than in the last case, the right treatment is to remove the cause of the putrefaction.

Drugs that have been used for this purpose are -

(1) Carbolic acid.

(2) Iodoform.

(3) Boric acid.

(4) Creosote.

(5) Eucalyptus.

(6) Thymol.

(7) Resorcin.

(8) Salicin.

(9) Bismuth salicylate.

(10) Salol.

(11) Sodium hyposulphite.

(12) Sodium sulpho-carbolate.

(13) Sulphurous Anhydride.

(14) Naphtol.

Charcoal has been employed, but when it is moist it is useless.

4. Drugs which dilate the vessels of the stomach. - The vessels of the stomach are very sensitive to irritation. They easily dilate upon mechanical irritation, and the presence of food, especially peptones, causes the vascularity of the mucous membrane to increase. Within limits greater vascularity is an advantage, for it not only favors the secretion of gastric juice, but it facilitates absorption. '

The substances which increase the vascularity of the stomach are all stomachics (except alkalies), diluted mineral acids, the drugs which have been already enumerated as irritants generally, and squill, digitalis, colchicum, senega, copaiba, gamboge, guai-acum, and veratrine. This is a very long list, and many of the substances in it are never employed for their irritant effect; in fact, the only ones in common use are the stomachics; the others are far too powerful; even small doses of them set up inflammation of the gastric wall, which is also produced by over indulgence in stomachics, as we constantly see in the gastritis induced by alcohol. The therapeutic indications for this class of drugs are the same as those for stomachics generally.