A heat of about 32 [degrees] Reaumur, constantly vaporizing the different fluids the circulation of which sustains life, the diminution they undergo would unfit them for their purposes, if they were not renewed and refreshed. The necessity of this renewal is what we call thirst. We think the seat of thirst is in the digestive system. When athirst (we have often felt the sensation when hunting) we feel distinctly that all the inhaling portions of the nostrils, mouth and throat are benumbed and hardened, and that if thirst be sometimes appeased by the application of fluids to other parts of the body, as in the bath, the reason is that as soon as they are absorbed they hurry rapidly to the seat of the evil and become remedies. VARIETIES OF THIRST. Looking at the subject in all its bearings we may count three varieties of thirst: latent, factitious and permanent. Latent or habitual thirst, is the insensible equilibrium established between transpiratory vaporization and the necessity of supplying what is lost. Thus, though we experience no pain, we are invited to drink while we eat, and are able to drink at almost every moment of the day. This thirst accompanies us every where, and is almost a portion of our existence. Factitious thirst is peculiar to man, and results from the instinct which impels him to seek in drink the strength he needs. It is an artificial enjoyment rather than a natural want. This thirst is really governless, because the fluids we take have the faculty of reviving it, and this thirst becomes habitual, makes drunkards in every country. The consequence is, that they drink as long as liquor lasts, or until they are utterly overcome. When, on the other hand, thirst is appeased by pure water, which seems the most natural remedy, we never drink more than we actually need. Hardening thirst is the result of the increase of the want, and of the impossibility to satisfy latent thirst. It is so called because it is accompanied by hardness of the tongue, dryness of the palate, and a devouring heat in all the body. The sensation of thirst is so intense, that in all tongues it is synonymous with excessive desire, and irrepressible longing: thus we thirst for gold, wealth, power, science, &c., expressions which never would have become common had men not have been athirst and aware of their vengeance. Appetite is pleasant when it does not reach the point of hunger. Thirst is not so, and as soon as we feel it we are uncomfortable and anxious. When there is no possibility of appeasing it, the state of mind is terrible. To compensate us for this, the sense of thirst procures us great pleasure; and when great thirst is appeased, or a delicious drink is offered to one moderately athirst, the whole papillary system is aroused, from the tip of the tongue to the extremity of the stomach.