This agency is merely a combination of those already treated of; but it affords so ready and efficient a method of obtaining their conjoint influence, that it merits a distinct notice. Exercise steadily maintained, pure air, and a favourable mental condition, are the real tonic agents which give to travelling the powerful curative influence exerted by it in affections complicated with, or essentially consisting in debility, whether of the whole system, or some one or more of its parts. But, to be useful, it must be properly conducted. To jump into a railroad carriage, or a steamboat; to be whirled in crowds from point to point, with headlong rapidity; to lodge in densely thronged hotels, and swelter all the night in close apartments; to be ever on the anxious watch for a good position, or any position at all, in the immense competition of the masses; to eat hurriedly anything which is set before you, and at times adapted not to your own convenience, but to that of the transporting party; often, in the onward rush, to pass nights without sleep, or with insufficient sleep, upon the road or the stream, and in an atmosphere contaminated with human exhalations; this is not relaxation and amusement; it is labour, often very fatiguing, vexatious, and exhausting labour; and it is no wonder that invalids, who travel thus, return weaker than when they started, and with very discouraging impressions as to the remedial virtues of travelling. All this should be reversed. There should be no hurry, no bustle, no anxiety or struggle. Arrangements should be made for quiet movement on foot, in a carriage, on horseback, or in two or more of these methods successively. The lodgings should be comfortable and airy, and a due amount of sleep procured. The meals should be taken as regularly as possible, eaten slowly, and of wholesome food. With a little care and forethought in regulating these points, the happiest effects may be hoped for. The charms of rural scenery and rural sounds, the frequent novelties, the succession of interesting incidents, the changing personal intercourse, the sweetness of repose after moderate fatigue, light and agreeable reading in the intervals of rest, the various gratifications of the passing day, the as varied hopes and plans for the morrow; perhaps a short sojourn in some way-side inn, with charming scenery and cool shade without, and cleanliness, neatness, and a cordial welcome within; perhaps a longer abode in some place of more general resort, by the sea-shore, or near some mineral spring, for example, where salt-bathing or chalybeate waters may superadd their tonic effect to that of cheerful social intercourse; all these genial influences combine, with the sustained exercise and uncontaminated air, to elevate and support the physical functions, and often serve to restore energy to a debilitated frame, upon which medicines have been tried in vain. In the debility of convalescence; in that resulting from an overstraining of the mental and corporeal functions in the eager pursuits of business or ambition; in various chronic inflammations of the internal organs, in which the local mischief is sustained by a want of due energy in the system to institute a restorative course; in the nervous affections, particularly the neuralgic, in which the nervous centres are enfeebled in the general weakness, and unable to resist irritating or otherwise disturbing causes; in the torpor of stomach, liver, and bowels, which are so often met with conjointly in dyspeptic disease; in such cases as these, it is, that we may expect good from travelling. To obtain its full advantages, it is sometimes necessary to persevere long; and a journey of six months, or of one or two years, will often completely accomplish a cure, which, with a shorter continuance of the same means, would be only partial or temporary.

Compressed Air as a Remedy. Dr. de Vivenot has ascertained, by a series of experiments, that by exposure daily to the influence of compressed air, as in a diving machine for example, the capacity of the lungs becomes enlarged. This increase of capacity amounted in himself and others, after a daily exposure for an hour or two, continued for three months, to the compressed air of a chamber, to 3.36 per cent., or about one-thirtieth of the whole capacity of the lungs. Nor was this condition transitory, as the augmentation was found almost undiminished a month after the cessation of the experiments. To this enlarged capacity was added an increase of elasticity of the pulmonary tissue, and of the power of the respiratory muscles. The surface, moreover, of the air-cells is brought into contact, in a given time, with a greater amount of air. Great therapeutic advantages might be expected from this kind of tonic influence, which is especially applicable to cases of emphysema, atelectasis, tuberculosis, dyspnoea from pleuritic exudation, etc. (Arch. Gen. de Mid., Nov. 1865, p. 611.) - Note to the third edition.