As far as it extends, this classification seems to be founded on correct data. The smaller divisions are natural. Thus Evacuants are grouped according to the part of the system at which the evacuation is made. General Stimulants are divided into those which are transitory in action, and those whose effect is permanent, as Tonics. Dr. Duncan is concerned only with the ultimate effect, and enters into no theory respecting the action of Tonics. I regard them as medicines acting primarily in the blood, and, applying my terms with a view to the _modus operandi_, I would restrict the term Stimulant to medicines acting on the nerves, whose effect is transitory. The great fault of this arrangement is the omission of the very important class of Alteratives. We have medicines which increase secretion; medicines which exalt or diminish the vital energy; but where are the remedies which act in the blood? Where, for example, shall we place such medicines as Mercury, Arsenic, and Iodine, which neither act by eliminating, nor by stimulating, nor by depressing, but appear to counteract in the blood the agency of certain morbid poisons? In an arrangement founded on ultimate effect, they should be grouped in a class as Alteratives, as medicines which result in _altering_ for the better the condition of the system. Both Dr. Duncan and Dr. Murray seem to have thought that no medicines could act in the fluids but such as have a well known chemical effect upon them. It cannot be that medicines should be able to affect the nerves, and to influence the glands, in divers ways, but that none should exert any action upon the blood, a most susceptible and changeable fluid, the medium of nutrition, the source of all the tissues, the "_fons et origo_" of disease. It is only very lately that authors have begun to recognise and include in their arrangements the class of blood-medicines, which seem to me to be considerably more important than any other. Having shown thus what appear to me to be the correct bases upon which an arrangement of this kind should be constructed, I shall quote as another specimen the classification of Dr. John Murray, but mentioning only its most prominent details. DR. MURRAY. GENERAL STIMULANTS. _Diffusible_ {Narcotics. {Antispasmodics. _Permanent_ {Tonics. {Astringents. LOCAL STIMULANTS. Evacuants, Irritants. CHEMICAL AGENTS. MECHANICAL AGENTS.