Perfectly normal healthy teeth consist of a hard, brilliant external coat, the enamel, which opposes great resistance to acid and decomposing substances. But unfortunately the enamel is very sensitive to changes of temperature and easily cracks, thus admitting to the bony part of the teeth such deleterious substances and leading to their destruction. The bulk of the tooth consists of a porous mass of bone which is easily destroyed, and thus the entire set may be lost. Hygienic perfumery is able to offer to the public means by which a healthy set of teeth can be kept in good condition and the disease arrested in affected teeth, and by which an agreeable freshness is imparted to the gums and lips. While true perfumes may be looked upon as more or less of a luxury, the hygiene of the mouth is a necessity; for we have to deal with the health and preservation of the important masticatory apparatus which is necessary to the welfare of the whole body, so that the æsthetic factor occupies a secondary position, or rather results as a necessary consequence from a proper care of the mouth. With no other hygienic article have so many sins been committed as with those intended for the teeth; we have had occasion to examine a number of tooth powders, some of them very high-priced, which were decidedly injurious. Thus we have known of cases in which powdered pumice stone, colored and perfumed, has been sold as a tooth powder. Pumice stone, however, resembles glass in its composition and acts on the teeth like a fine file which rapidly wears away the enamel and exposes the frail bony substance. It needs no further explanation to prove the destructive effects of such a powder on the teeth. Many person prize finely powdered wood charcoal as a tooth powder, and to some extent they are right. Wood charcoal always contains alkalies which neutralize the injurious acids, besides traces of products of dry distillation which prevent decomposition. But these valuable properties are counteracted by the fact that charcoal is always more or less gritty, or, being insoluble, will lodge between the teeth and form the nucleus for the lodgement of other substances. In compounding articles for the mouth and teeth—tooth powders and mouth washes—the objects aimed at are to neutralize the chemical processes that injure the teeth and gums, and to restore freshness and resisting power to the relaxed gums and mucous membranes. Remnants of food left in the mouth after meals soon develop acids which attack the teeth; they are neutralized by basic substances or alkalies which counteract them. The formation of organic acids from food remnants is caused by microscopic fungi (schizomycetes) which adhere to the teeth (so-called tartar) in the absence of cleanliness; against these parasites there are at our disposal a number of substances which kill them rapidly and thus for a time arrest the process of decomposition; they are therefore called antiseptics.