Acids, mineral and vegetable.

Acid salts. Alkalies. Ethereal bodies Ether.

Chloroform, etc. Pungent substances Mustard.

Horseradish.

Ginger. Pyrethrum. Mezereon. Tobacco, etc. Rhubarb. Cubebs. Nauseants. Tartar emetic, etc.

Specific Sialagogues.

Jaborandi. (Pilocarpine.)

Muscarine.

Physostigma. (Physostigmine.)

Tobacco.

Compounds of Iodine.

Mercury and its compounds.

Reflex Sialagogues. - Acids, ether, ginger, horseradish, mezereon, mustard, pyrethrum and rhubarb, all produce salivation by stimulating the salivary glands reflexly through the nerves of the mouth.

The effect produced by reflex or topical sialagogues is not the same for each. Ether and dilute acids produce a thin, watery saliva, but alkalies cause the secretion of a thicker and more viscid saliva: the former appearing to affect chiefly the chorda tympani, and the latter the sympathetic.

Nauseants, such as tartar emetic, stimulate the glands reflexly through the vagus.

Mixed Sialagogues. Mercury probably acts partly upon the gland structures and partly reflexly through the nerves of the mouth. Tobacco, when smoked or chewed, probably acts both reflexly and specifically. Iodide of potassium may act partially as a reflex sialagogue, for it is secreted in the saliva, and it therefore comes to be present in the mouth more or less persistently. It is probable, however, that it acts also upon the gland-structures, though it has not been determined whether the secreting cells or the nerves are chiefly affected.

Specific Sialagogues. - The peripheral ends of the secreting nerves in the gland itself are stimulated by pilocarpine or jaborandi, muscarine, nicotine and physostigmine, so that secretion is induced by the injection of these substances into the blood even after all the nerves going to the gland have been cut.

In large doses these substances paralyse the ends of the secreting nerves, so that irritation of the chorda tympani will no longer cause secretion. Physostigmine and nicotine, besides acting on the peripheral terminations of the secretory nerves, stimulate the central ends of those nerves so that section of the chorda tympani greatly lessens the secretion which these substances cause, although it may still persist from the effect of the drug upon the peripheral terminations.

The peripheral action of physostigmine and nicotine is, however, much less marked than that of muscarine and pilocarpine, so that the secretion caused by the two former after the nerves have been divided is very much less than that produced by the latter.

Physostigmine acts also on the sympathetic nerves, producing contraction of the vessels at the same time that it is stimulating the secreting centre in the medulla. In consequence of this double action, secretion is rapid at first; it, however, diminishes very quickly or ceases entirely, the circulation being so much lessened by the contraction of the vessels that the glands do not get sufficient supply of new material to go on secreting.