DIVISION IX.-DRUGS ACTING ON THE DIGESTIVE SYSTEM

A. Drugs acting on the Teeth.-For cleansing the teeth, powders are commonly used, but soaps, semi-liquid and liquid dentifrices are occasionally employed. Chalk, which acts mechanically, constitutes the basis of most tooth powders, and charcoal, which, however, may abrade the enamel, is also sometimes used for its mechanical effect. In order to prevent the decomposition of food lodged between the teeth, antiseptics, such as quinine, borax and phenol, are often used as ingredients of tooth-powders. Astringents such as kino are employed when the gums are inclined to bleed. As iron is apt to blacken the teeth and mineral acids and alum are injurious to them, it is advisable that these drugs should not be used as gargles for long periods, and that when prescribed internally they should be taken through a glass tube.

For the relief of toothache local anodynes such as creosote or phenol may be employed on absorbent cotton, which is inserted into the cavity of the carious tooth. There is some danger of damage to the dental pulp, and to prevent injury to the gums and mouth a pledget of plain, should be placed over the medicated, cotton.

B. Drugs acting on the Salivary Glands.-Drugs which increase the amount of saliva are called Sialogogues; those which diminish it, Antisialogogues. The saliva is derived from the secretion of the parotid, submaxillary and sublingual glands and the muciparous glandules of the buccal cavity, and the secretions produced by these different glands vary somewhat in their physical, properties, especially in the degree of their viscidity. The function of the submaxillary gland and the influences affecting it have been especially studied, and it is known that the gland is largely under the control of the chorda tympani nerve, some of whose fibers are of a vaso-dilator character, and thus secondarily influence the glandular secretion, while others affect the latter directly. This nerve, which has its center in the medulla, may be reflexly excited by stimulation of various nerves, and particularly the gastric branches of the vagus and the lingual and buccal terminations of the glosso-pharyngeal and gustatory nerves. The gland has also a nerve-supply from branches of the

cervical sympathetic trunk which are vaso-constrictor in character. The secretion of saliva appears to occur only when impulses reach the gland cells through the chorda tympani or through the cervical sympathetic fibers.

1. Sialogogues acting either on the secretory cells or upon the terminations of the nerves in them. Of these, pilocarpus has been the most carefully investigated, and it has been shown that it acts on the terminations of the secretory nerves-the minute fibrils which ramify between the epithelial cells and perhaps even enter them. It is found that its action is not at all interfered with by section of all the nerves supplying the maxillary glands; also that it acts when injected directly into the gland but is prevented from entering the general circulation. When pilocarpus has been administered, the effect, which stimulation of the chorda tympani or of the sympathetic produces, is only such as can be readily explained by the vascular effects.

Sialogogues belonging to this class are―

(1) Pilocarpus.

(2) Iodine.

(3) Mercury.
(4) Physostigmine.

The last two probably act also by stimulating the medullary center, for section of the chorda tympani markedly lessens the secretion. Physostigmine also soon tightly contracts the vessels of the gland, thus checking secretion.

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

(a) Those stimulating the gustatory and glosso-pharyngeal nerves in the mouth (1) All Acids and Acid salts. (4) Ether.

(2) Chloroform.

(3) Alcohol.

(5) All pungent substances, as pyr

(b) Those stimulating the vagus in the stomach:

ethrum, mustard, ginger, etc.

Most emetics, particularly Antimony and Ipecac.

3. Antisialogogues acting either on the secreting cells or the terminations of the nerves in them.-Atropine acts directly on the gland as is shown by the fact that it prevents any increase of salivary secretion on stimulation of the chorda, although the vessels dilate as usual. It appears to act on the terminations of nerve fibers in the gland cells but this action is limited to certain definite terminations, since the sympathetic secretory nerve fibers are not paralyzed, and it has been ascertained that not all the fibers of the chorda tympani are acted

upon. Atropine would seem, then, to act upon the terminations of the secretory fibers, and to leave all others unaffected.

Antisialogogues falling under this heading are

(1) Belladonna, (2) Hyoscyamus, (3) Stramonium and their alkaloids.

4. Antisialogogues acting reflexly by depressing the peripheral ends of afferent nerves. Such are alkalies, opium, and any substances diminishing irritation of the mouth. Opium also has a depressing action on the medullary center.

Therapeutics. A deficiency in the amount of saliva secreted is a prominent feature of belladonna poisoning, although it is most commonly met with in fevers, the mouth becoming extremely dry and the patient suffering from thirst. Remedies which relieve this and impart a sensation of coolness are known as Refrigerants. In fever acid drinks, such as lemonade, and beverages containing carbon dioxide gas are of service as sialogogues. For the condition known as "dry mouth" which is probably of nervous origin, pilocarpus has been employed, and this is also useful in relieving the dryness caused by belladonna or its alkaloid. Excessive salivary secretion is seldom met with except as a symptom of poisoning by such drugs as mercury, iodine and pilocarpus. In some forms of indigestion the saliva acquires a very disagreeable taste, or perhaps the secretion may become diminished; but here the correction of the difficulty is to be sought in the improvement of the digestion.

C. Drugs acting on the Stomach.-In the present state of our knowledge it is not possible to speak with accuracy of the special action of many of the drugs affecting the stomach, and it will therefore serve the most useful purpose to divide this class of drugs into those affecting the secretion of gastric juice as a whole, the secreted contents, the vessels, nerves, and movements of the stomach, and, lastly, those which are emetics.

1. Drugs increasing the amount of gastric juice secreted. These are usually called Stomachics, and they include a large variety of agents. The secretion of gastric juice is reflexly augmented by all bitter and aromatic substances, which likewise increase the appetite, as well as by stimulants to the mouth. Indeed, the smell and sight of food constitute the most powerful stimulant to gastric secretion, and substances of agreeable flavor cause a marked increase in it by reflexes from the mouth and nose. The simple presence of food in

the stomach also tends to promote the flow. The aromatics appear, like other volatile oils, to cause an irritation, hyperæmia and increased secretion and peristalsis, with consequent improvement in digestion and absorption. It is thought probable, though this has not been proved, that bitters cause an irritation, leading reflexly to the same results. Their effects are, however, no doubt largely due to their taste, which is very lasting.

The drugs which increase the flow of gastric juice are—

(1) Aromatics.

(2) Bitters.

(3) Alcohol.

(4) Ether.

(5) Chloroform.

(6) Pungent substances, generally.

Therapeutics. Stomachics are extensively employed to favorably modify the digestive process in various functional disorders.

2. Drugs decreasing the amount of gastric juice secreted.

(1) Mineral acids. (2) Acetic acid.

(3) Alcohol, Ether and Chloroform, in large doses.

Therapeutics. These drugs, however, are never given for this purpose. It should be noted here that acids and alkalies have opposite effects as regards the gastric juice and the saliva. While acids diminish the secretion of the gastric juice, which is acid, they increase that of the saliva, which is alkaline; alkalies, on the other hand, diminish the secretion of the alkaline saliva, but increase that of the acid gastric juice.

3. Drugs altering the composition of the gastric contents.-The reaction of the gastric contents may, of course, be modified by acids and alkalies. In instances of difficult digestion due to a deficient secretion of hydrochloric acid, diluted mineral acids are often prescribed, and they should be taken about two hours after eating, so as not to interfere with the secretion of the natural acid. If, on the other hand, there appears to be an excess of acid in the stomach, alkalies are ordered at meal times, and sodium bicarbonate is the one generally selected, although either the heavy or light magnesium oxide is preferable. When it is thought that secretion of pepsin is at fault, this is administered, and it is customary to prescribe it with diluted hydrochloric acid. In order to prevent fermentation and putrefaction in the stomach, antiseptics are employed. In all varieties of indigestion it should be borne in mind that it is of much greater im

portance to remove the primary cause of the trouble than to endeavor to modify the composition of the gastric contents.

Drugs which have been used for this purpose are

(1) Phenol.

(2) Iodoform.
(3) Boric acid.
(4) Creosote.

(5) Eucalyptus.

(6) Thymol.

(7) Resorcinol.

(8) Salicin.

(9) Bismuth subsalicylate.

(10) Phenyl salicylate.

(11) Sodium phenolsulphonate.

(12) Sulphurous anhydride.

(13) Naphthol.

(14) Charcoal.

Moist charcoal has been considered by many to be useless, but it has been shown that it is capable of absorbing the gases from decomposing matter almost as readily as when dry.

4. Drugs which dilate the vessels of the stomach.-The vascularity of the stomach is very readily affected. Thus, mechanical irritation, such as results from the presence of food, and particularly peptones, causes a considerable dilatation of the vessels. Such increased vascularity, if not excessive, is advantageous, since it tends to promote absorption, as well as gastric secretion. The substances which increase the vascularity of the stomach are: all stomachics, excepting alkalies, diluted mineral acids, the drugs which have been already enumerated as irritants generally, and squill, digitalis, colchicum, senega, copaiba, gamboge, guaiac and veratrine. Most of these, however, produce, even in small doses, too powerful an irritant effect to be of service in this regard, and practically the only class of drugs, much employed to increase gastric vascularity, is the stomachics. Even these may induce gastritis, if used to excess, as is constantly seen in the case of alcoholics.

Gastro-intestinal irritants.-It will be found that in the description of the action of drugs a large number are designated as gastro-intestinal irritants. Caustic potash and mineral acids such as nitric and sulphuric acids are very powerful agents of this class. There is naturally a great variation in the severity of the effects of different gastro-intestinal irritants, and it is worthy of note that many of them have no action on the mouth.

5. Drugs which contract the gastric vessels.-These have already been mentioned as being generally astringent. As they are much more frequently employed for intestinal disorders, than for those of the stomach, they are considered later (see p. 626).