illustration of this fact, for the roots of this useful plant which have been so greatly improved by culture, are in their wild state both small and _bitter_.[143] Gummy matter, which seems to result from the first change of the sap, is undoubtedly rendered more digestible and nutritive by the presence of a _bitter_; pure gum is not very much disposed to yield to the assimilative functions; “it frequently passes through the bowels,” says Dr. Chapman,[144] “very little changed, as I have witnessed a thousand times.” We see therefore the value of the bitter principle, in the economy of the _Lichen Islandicus_, which is intended as the food of animals in northern latitudes; we are told that boiled linseed constituted the sole diet of the people of Zealand during a scarcity of long continuance, on which occasion, symptoms of great debility occurred, attended with those of dyspepsia; so again Professor Fritze, in his Medical Annals, states that vegetable mucilage, when used as a principal article of diet, relaxes the organs of digestion, and produces a viscid slimy mucus, and a morbid action in the primæ viæ, an effect which analogy shews might be obviated by the addition of bitter extractive. For the same reason animals that feed in marshy lands, on food containing but little nourishment, are best defended from the diseases they are liable to contract in such situations by the ingestion of bitter plants.[145] Upon these occasions nature is very kind, for the particular situation that engenders endemic diseases is generally congenial to the growth of the plants that operate as antidotes to them. I have offered these views upon the subject of _Bitter Extractive_, from a conviction that they will essentially contribute to the establishing of just and philosophical notions, respecting the necessity and _modus operandi_ of many vegetable tonics. As the action of tonics is gradual, so their operation is not followed by that exhaustion consequent upon the use of diffusible stimulants. The substances which compose the class of tonics are derived from the vegetable and mineral kingdoms; those of the former are generally bitter, and produce their effects by a primary action on the stomach, and are not absorbed into the circulation, as experiments upon _Bitter Extractive_ have most fully demonstrated; those derived from the mineral kingdom, comprehending several of the metals, appear in some instances to pass into the circulation, although several of them, like the vegetable tonics, act primarily on the _primæ viæ_; I apprehend this observation applies to the _nitrate of silver_, which certainly possesses considerable powers as a tonic in certain cases of dyspepsia, for which it may perhaps be indebted to the bitterness which distinguishes it. AROMATICS.