Any solid substance which excites the mucous surface of the mouth, as the natural food,--or even the act of mastication alone,--will suffice to bring on the secretion of saliva. An irritant substance, as Ginger, or Pyrethrum, tends especially to cause this secretion when masticated. Catechu and Betelleaf are chewed for this purpose by the natives of the East. Such a stimulation of the salivary glands may be advantageously resorted to on the counter-irritant principle in obstinate cases of head-ache, ear-ache, or tooth-ache, or in neuralgic or chronic rheumatic affections of the face. When the quantity of the saliva is thus increased, it should not be rejected, but always swallowed when possible; for this secretion is apparently useful in the stomach, and in some way essential to the proper carrying on of the digestive process. The chewing of Tobacco, Betel, and other substances, is frequently found useful by sailors on long voyages, and is adopted as a preservative against the dysentery and diarrh[oe]a with which they are so often affected. This advantage is to be attributed to the increase in the salivary secretion. On the other hand, we find that the practice of constant spitting is productive of very injurious effects; and it is more than possible that the pale faces, lank figures, and dyspeptic maladies, which are so common among the American people, may be due in part to the prevalence of this habit among them. These topical irritants and masticatories are not true Eliminatives. There are also some medicines which by another topical action may occasionally produce salivation. These are Sedatives. Hydrocyanic acid, Digitalis, and nauseant medicines, may act locally so as to paralyze the muscular fibres by which the constriction of the salivary ducts is maintained, and thus allow the secretion to pour out uncontrolled into the cavity of the mouth. _True or Eliminant Sialagogues._--These are medicines which are actually excreted from the blood by the salivary glands, and which increase their natural secretion while passing through them. Mercury is the most important of these. When given to a considerable extent, it causes soreness and redness of the gums, and profuse salivation. It probably increases the amount of saliva even before this soreness is produced. It is not given for the purpose of producing salivation, but in cases where the full action of Mercury is desired this symptom is made use of as a sign that the medicine has taken full effect upon the system. If we permit it to be carried to too great an extent, sloughing of the gums and other dangerous results may be produced. In some rare cases salivation has followed the administration of Iodine. It is also not an unfrequent symptom of chronic poisoning by Lead. In cases of salivation by these Eliminative medicines, the substance which has caused the increased secretion may be, and has been, discovered in the saliva by chemical tests. They are therefore true Sialagogues.