Such then appears to be the _modus operandi_, and such are the chief applications, of the remedies belonging to the order of General Stimulants. Those of the next order exert an action of the same kind, but their field of operation is on a more confined scale. ORD. II. SPECIAL STIMULANTS. (Strychnia; Brucia; Toxicodendron; Ergot of Rye; Borax; Rue.) These are medicines which pass from the blood to the nerves or nerve-centres, and act so as to exalt the energy of particular nerves or sets of nerves. They do not affect the whole nervous system, but they operate on one set of nerves in the same way that General Stimulants operate on all, though usually with greater energy. The causes of such a localized action are hid in obscurity; but it has already been hinted that they may perhaps be partly accounted for by the differences in chemical or mechanical structure existing between different parts of the nervous system. Strychnia, the alkaloid and chief active principle of Nux Vomica, acts as a Special Stimulant, chiefly to the spinal cord and the nerves that proceed from it. Its operation is mainly exerted upon the motor branches. Thus in large doses it causes a spasmodic and powerful contraction of the muscles of the trunk, and may even produce death by rendering respiration impossible. Its action is propagated from a motor nerve to a muscle, and is kept up for some time. In small doses it is useful in certain cases of paralysis. Two things are necessary in order that it may act efficiently. The muscles of the part must be whole and sound; for if destroyed by excessive atrophy or fatty degeneration, they cannot be roused by any stimulus. The nerve, too, and the centre from which it originates, must be sound, or else the medicinal impulse cannot be conducted along it. These two conditions can only concur in paralysis from disuse, _i.e._ when the incapacity to move a limb depends merely upon its having long been in a state of inactivity, but when the lesion of the centre which caused the paralysis has at length sufficiently healed, and the nerve is now in a fit state to conduct a motor impulse. Strychnia has no operation on the intellectual functions; neither does it act upon the sympathetic nerves of the heart and arteries, so as to quicken the pulse like ordinary stimulants. It exalts sensibility as well as irritability, but not so powerfully. It is a special Stimulant to the motor and sensory nerves throughout the body. Acting upon the spinal cord, it tends thus to exalt reflex action, which is derived from that centre. In small doses it appears to promote digestion, and may perhaps act upon the ganglionic nerves supplied to the stomach. Brucia, which is the other alkaloid of Nux Vomica,--and the leaves of the Rhus Toxicodendron,--resemble Strychnia in their action, but are less powerful.