Stimulation, as here understood, is the exaltation of any or of all the vital functions above the state in which they may happen to exist, at the time when the stimulating measure is resorted to. There is a vast diversity in this process. It differs in direction, degree, duration, and character. Perhaps the most convenient primary division of it is into general and local; the former being felt, to a greater or less extent, throughout the body, the latter confined originally to a particular part or organ.

A property common to all stimulation is, that it is followed, in the ordinary state of the system, by a degree of depression bearing some proportion to the previous excitement. There are conditions of temporary prostration, in which stimulation may put the system in the power of resuming its ordinary grade of action without subsequent depression; but these do not come within the general rule. The depression is dependent upon the temporary diminution of excitability, resulting from excessive action. If the stimulant influence be continued, it follows, as a consequence of the diminished excitability, that a greater amount of the stimulant agent must be employed to produce the same effect, and the excitability is thus still further diminished; until, in the end, the system refuses entirely to respond to the ordinary healthy excitants, and morbid and often fatal debility results This is an evil against which it is necessary to be constantly on our guard, in the use of stimulant measures. Another, scarcely less important, is the production of inflammation by the excessive or repeated excitement to which the stimulated organ or system is exposed.

1. General Stimulation

It is barely possible that stimulation should be absolutely universal In whatever degree the functions generally may be excited, there is almost always some one or more that become de-pressed, or remain quiescent. Stimulation may be considered general, when any one of the vital properties or functions which belong to all parts of the frame is exalted, as contractility or nutrition; or when one of the anatomical systems which pervade the whole body is excited into increased action, as the circulatory or nervous. In such cases, the excitement is felt throughout the frame, though not in every function.

The lowest grade of general stimulation is that produced by astringents, which operate on the organic contractility, and produce a general condensation or shrinking of the tissues. Tubes and orifices are thus contracted, the flesh becomes firmer, and the pulse somewhat more tense. The therapeutic applications of this power of astringency, with the requisite cautions, will be hereafter fully considered.

Somewhat higher in the scale of general stimulation is the action usually denominated tonic. This is a moderate increase of the vital functions generally, produced rather slowly, and lasting for a considerable time. It is of vast importance in the treatment of moderate or chronic debility. For an account of its special applications, the reader is referred to the second part of the work. Among the agents by which it is effected is a class of medicines denominated tonics, which may act directly on the whole system, or especially on the digestive function, thereby enriching the blood, and making that Quid the immediate excitant. Some medicines probably also give tonic power to the blood by a direct action on that fluid. Such are the chalybeate?. But there are other very important tonic agents besides medicines. Cold operates in this way secondarily, through the reaction which follows its direct de-pressing influence. A wholesome and nourishing diet, succeeding an impoverished one, and pure fresh air with those who have been confined to a close and vitiated atmosphere, have a powerful tonic operation. So also has moderate physical exercise, under similar circumstance.

previous deprivation. Gentle electrical excitation may be placed in the same category. Mental influence*, moreover, have great effect No tonic is, under many circumstances, more efficient than the cheering influence of social pleasures, domestic enjoyment, and a gentle exercise the intellectual faculties, and all the kindlier emotions.

A quicker and more rapid stimulation is sometimes distinguished by the name of diffusible. It usually affects more or less, at the same time, the functions both of organic and animal life; though, as proceeding from one cause it may be more especially felt in the circulation and its dependent functions, from another, in the nervous system. This special direction is sometimes so far exclusive as to justify the division of diffusible stimulants into those operating more particularly on the circulation, and those upon the cerebro-spinal functions. It will be found, hereafter, that this distinction serves as the basis of an arrangement in the plan of classification which I have adopted. For want of a better name, the medicines acting on the circulation especially, with little tendency to the nervous system, may be denominated arterial stimulants.

Stimulants which act chiefly on the nervous system may diffuse an apparently equable action over the whole of that system, or may concentrate their influence especially on the brain. The former may be called nervous stimulants, though more commonly designated as antispasmodics; the latter I propose to call cerebral stimulants, preferring this title to that of narcotics, which has reference to the property of stupefying, that belongs also to medicines of wholly different powers. It will be perceived hereafter that the above arrangement of stimulant medicines is not only natural, in relation to their physiological effects, but has also an important practical bearing.

Other influences besides those properly medicinal are susceptible of very useful employment in reference to general stimulation. Heat and electro-magnetism are agencies of this kind; and stimulating food is yet more important. These will be fully treated of under Special Therapeutics.

2. Local Stimulation

Local stimulation may have the effect of merely irritating or inflaming a part; or of exciting it to an increased performance of its peculiar function.

In the former case, the object is usually to act revulsively, or to produce general stimulation through the sympathy of the system with the part affected. The agents employed for either purpose, so far as the external surface is concerned, are the rubefacients, epispastics, and escharo-tics Occasionally, however, the object is entirely local. The vessels of a part may become relaxed and congested with blood, and, in conse-quence, an imperfect sort of inflammation may be sustained; or there may be ulceration, and the surface too feeble to take on the action necessary for the healing process. In either case, local stimulation sometimes answers an excellent purpose in removing the evil.

But still more frequently this remedial process is employed for the increase of function. The surface may be pale, thy, and inactive; the muscles may be enfeebled to paralysis; the senses of smell, taste, and touch may be imperfect from weakness; digestion may be feeble, and the bowels costive from deficient secretion, or want of due peristaltic movement; the liver, kidneys, or other secretory glands may be inert. The means used to restore the weakened functions are medicines and other remedies, having a special influence over the functions severally. Hence the use of friction to the surface; the hot bath; the cold bath used with a view to reaction; diaphoretics; errhines: masticatories; gastric stimulants, such as bitters, aromatics. and the mineral acids: emetics; cathartics; diuretics; expectorants: emmenagogues; and chola-gogues to excite the liver, as mercury and nitromuriatic acid. Hence the employment of ergot to stimulate the uterus to contraction.

Sometimes a local stimulant is employed to produce general depres sion; as in the case of the hydragogue cathartics, which, though they stimulate the secretory function of the bowels and promote the peristaltic movement, depress the system in consequence of the depletion they produce.