Some of these appear to be universal, such as heat and electricity; but the greater portion, and perhaps all which come strictly under the denomination of medicines, exhibit a special tendency to one or the other of the two great pervading systems or apparatuses of the body, the circulatory, namely, and the nervous. As those which have a tendency to the circulation operate directly rather upon the arterial than the venous side of it, I name them arterial stimulants. Those acting specially on the nervous system may be called cerebro-spinal stimulants.

1. Arterial Stimulants are scarcely susceptible of further profitable subdivision, and therefore constitute one of the ultimate classes. They are characterized especially by their property of increasing the action of the heart and arteries, and, along with this effect, and probably consequent upon it, of causing an elevation of the animal temperature.

2. Cerebro-spinal Stimulants

I do not wish, by the use of this term, to intimate that the remedies so called act exclusively on the brain and spinal marrow; they may possibly, and probably do, in some instances, affect the ganglionic system, and, indeed, the whole nervous substance wherever they may meet with it. There is a marked difference between the members of this subdivision. Whilst some appear to operate equably upon the whole nervous system, showing no special influence over the proper cerebral functions, others act with great energy on the brain, as evinced by their power of deranging sensation, voluntary motion, consciousness, and the various intellectual and emotional functions. The former I denominate nervous stimulants, the latter cerebral stimulants. Besides these two sets of cerebro-spinal stimulants, there is at least one medicine which acts especially and powerfully on the spinal marrow, and for which a distinct class may be formed under the name of spinal stimulants. These three are all ultimate classes.

a. Nervous Stimulants, characterized by a special but equable influence over the nervous system, generally stimulate in some degree, though not necessarily, the circulation also. They are sometimes called nervines, and not unfrequently antispasmodics.

b. Cerebral Stimulants, with more or less influence on the circulation, and sometimes a powerful influence, are peculiarly characterized by their control over the special cerebral functions. They are equivalent to the stimulant narcotics of other writers, and embrace some of the most energetic articles of the materia medica, such as alcohol and opium.

c. Spinal Stimulants act specially, so far as their operation is known, on the reflex motor function.