If there be one change in the blood to which, more than to any other, the substances which enter it are liable, it is certainly the process of oxidation. Free oxygen is continually entering the blood through the air-cells of the lungs. The formula for Quina is C_{20}H_{12}NO_{2}. Adding to this 45 atoms of oxygen, we could make out of it one atom of Taurine, together with 16 of Carbonic acid, and 3 of water. C_{20}H_{12}NO_{2} + 45 O = C_{4}H_{7}NO_{10} + 16 CO_{2} + 5 HO. Thus it is conceivable that this and similar alkaloids may at the same time supply an important material to the blood, and serve as fuel to support the animal heat, by combining with oxygen and giving off Carbonic acid. I would not, of course, affirm that this actually does occur; but if it were to take place, we might gain, in this oxidation of Quina, some clue to the production of that quickening of the pulse and increase of the general temperature, which are affirmed by some to follow the ingestion of the alkaloid, even in small doses. But it is now sufficient for us if we have ascertained that there is naturally in the system, and in the blood, a substance which resembles Quina. We may be allowed to infer that the presence of the latter substance in that fluid would not be unnatural to it. Having dismissed the second of the minor propositions which relate to Tonics as Restorative medicines, we pass on to the third. Are Quina and the vegetable bitters necessarily excreted from the blood? It is not easy to answer this question with certainty, because it would be difficult to detect small quantities of this alkaloid in any of the secretions. But all that is known on the subject is in favour of a negative answer. A number of careful and elaborate experiments on the passage of medicines into the urine have been made by M. Wöhler, and in the long list of substances detected by him in that secretion, Quina is not mentioned. Neither has it been found in any other of the secretions. The same may be said of all the Tonic principles. There is no proof that they are necessarily excreted, but there is every reason to suppose that they may remain for a while in the blood. Let us then consider the last question. Can Quina, or substances like it, improve the condition of the blood when deficient in any of its natural materials. We know that it is capable of curing simple debility, ague, and remittent fevers. It appears that it has also been successfully used of late by Dr. R. Dundas, in large doses, in the treatment of typhoid or continued fever. Supposing it to be proved that this agent operates in the blood, does it remedy a disease by supplying something wanting, or by counteracting something present in that fluid? In fine, is it a Restorative or a Catalytic medicine?