It is just possible that the presence in the blood of this bile-product, the supply of which has been cut off by the hepatic disease, might have prevented the continual action of the Ague-poison. There is another fact which gives additional probability to such an idea. Another remedy of a different kind has been used in all the diseases in which Quina is admissible, proving in some cases superior, and in other instances second only to it in its beneficial action. This is Mercury; used in remittent and yellow fevers; of the first importance in dysentery; employed by Dr. Baillie in Ague, and pronounced by him to be in some cases superior even to Quina. In small doses it is frequently of use in cases of debility and scrofula. And Mercury is a Cholagogue; _i.e._ an agent which is known to have the effect of promoting the secretory function of the liver. Thus we may conceive that Mercury, not given in excess, or to salivation, may operate in a different way to produce the same end as Quina. One explanation would suffice for both. If this connexion between Tonics and the Bile were actually established, then we should be enabled to explain a matter which would otherwise seem difficult to understand,--how it is that small doses of Mercury may sometimes act as Tonics, though we know that the ultimate action of this medicine, like that of other Catalytics, is to deteriorate the blood. Even in scrofulous and enfeebled cases, small doses of blue pill or of Calomel are often signally useful; and not prejudicial, as is sometimes stated by those who confound their application with that of Mercury given in salivating doses. Under such a course, when judiciously enforced, we may see the dilated pupil contract to its normal size, and the pale enervated countenance become rosy and lively; and feel the weak compressible pulse to become hard and firm. Perhaps Mercury in such a case may be indirectly tonic, by restoring to the blood the natural tonic principle of the bile. It will be conceded that it is a great merit in a theory, when it succeeds in explaining at the same time a number of different things in a plausible way. It seems that this hypothesis of the connexion of Tonics with Taurine, or some such element of the Bile, is capable of so doing. I am very far from asserting that it is proved, or from supposing that it is at all likely to be so in the present state of our knowledge of the subject; but I think that if not evidently true, it appears at least reasonable. And it may be observed, that even should this idea be completely overthrown, which is neither impossible nor unlikely, there would still seem to be left ample evidence to prove that Quina and other vegetable bitters act on the blood on the restorative principle,--though in what exact way is uncertain. ORD. V. CHALYBEATES.