It should be observed, that the irritant action on the stomach of a large dose of a bitter medicine appears to have been the chief foundation of this frequent opinion of the stimulant action of tonics. The irritable stomachs of nervous persons are more easily affected in this way. Some too are met with who bear Tonics worse than others, on account of an idiosyncrasy or peculiarity of constitution. But this irritation, and the headache and febrile symptoms which succeed to it, do not surely constitute the proper action of a tonic medicine, which is found to operate most favourably when given in too small a dose to produce any thing like a stimulant effect. Nor do I think it proved that any true stimulants are capable of communicating a permanent tone to the system, or to any part of it. Dr. Ballard also, (in _Ballard and Garrod's Materia Medica_,) states that Tonics acts first upon the nerves, and through them on the muscular system. He opposes them to Sedatives, and ranks them with stimulants; quoting Strychnia as an example of a stimulant which gives tone to the muscular system. But, in the first place, this alkaloid is quite exceptional among stimulants; and further, the comparison with Tonics seems unnatural, inasmuch as the action of Strychnia is more or less immediate, not slow and permanent, and it evidently influences the spinal system of nerves in the first place. The results of large doses of Quina, in producing determination of blood to the head, ringing in the ears, and vomiting, seem to me to mark its action as an irritant poison, and not to be characteristic of Tonic medicines. (_Vide_ p. 91.) The action of Tonics has been more correctly defined by another able authority. "Tonics," says Dr. A. Billing, "are substances which neither immediately nor sensibly call forth actions, like stimulants, nor repress them, like sedatives, but give power to the nervous system to generate or secrete the nervous influence by which the whole frame is strengthened." This definition I would accept in a modified sense, considering that no permanent alteration in the nervous system can be produced without a primary impression on the blood. Dr. Billing further considers, that the supposed stimulant action of Tonics in some cases should either be attributed to the operation of the disease, or of some other medicine administered along with them; and that though in large doses they may sometimes produce a quick pulse with headache, and in other instances depression with nausea, yet that these effects should be ascribed merely to their irritating action on the stomach. On the whole, it seems to me that those authors who, in defining the action of Tonics, have commenced by saying that they act on the nervous system, have started with a mistaken notion; and I am more of the opinion of Dr. A. T. Thomson, who classes them as medicines which act on the muscular and sanguiferous systems.