This may arise from the absorption of the fluid parts of the saliva ; for it appears to be necessary for the due performance of the functions of the palate and the tongue, that the mucus should possess a certain degree of liquidity. The sensation of thirst is generally indicative of the necessity of a supply of fluid to the system generally ; for although thirst may be momentarily assuaged by wetting the mouth, or holding a thin fluid in it --yet it

can only be effectually relieved by conveying into the stomach a quantity of fluid sufficient to supply the deficiency. This supply is termed dilution, from the fact that the fluid is absorbed and carried into the blood, which it renders thin, and the

fluids themselves are called diluents.

Thirst, however, does not always indicate a deficiency of fluids in the circulating mass, and the tongue and fauces are occasionally dry and harsh whilst the sensation of thirst is absent. Some individuals never experience the sensation of thirst. Mr. Alcott, who lives entirely on succulent vegetables, states that

he has drunk no fluids for more than a year past, and that he never experiences the sensation of thirst --a similar case is mentioned by Sauvages, of an individual who never thirsted, and passed whole months of the hottest weather without drinking. It is well known that many warm-blooded animals such as mice, quails, parrots, rabbits, &c, drink but very little which is supposed to be owing to ;