In sea-water the more important saline constituents are the chlorides of sodium and magnesium, and the sulphate and carbonate of lime. Iodides and bromides are contained in minute quantity. Hence the effect of sea-bathing upon the skin and its peripheral nerves is more stimulating than that of ordinary water, an effect which is much heightened by the stroke of the waves (Wellenschlag).

The incoming wave beats more upon the upper part of the person, the receding wave upon the lower extremities, providing one of the best forms of douche-bath for such as are strong enough to bear it.

This wave-stroke is naturally more effective in some seas and on some coasts than on others. In the German Ocean (east coast of England) and in the Atlantic (south coast) it is much stronger than in the Baltic or the Mediterranean, and bathing at Cannes, for instance, is not to be compared in bracing effect with bathing at Brighton.

The temperature of the water is an important point in estimating the effect of any form of bath. The temperature of the sea varies less throughout the year than that of rivers: it is highest in the Mediterranean (72° to 80° F.), lowest in the Baltic (60° to 62° F.), and intermediate in the Atlantic (68° to 73° F.). It is higher in autumn than in summer, and hence, September is a good month for sea-bathing, though the wave-stroke is not then so forcible as it is earlier. The temperature of the water is often as much as 12° F. higher than that of the air, and at midday it is several degrees higher than in the early morning.

In considering the influence of sea-water, that of sea-air must not be wholly omitted. It contains more ozone, more moisture, and more salt than country air, with less carbonic acid, and usually less dust and foreign admixture; in fine weather the air is more clear and the sun-light more powerful at the coast than inland, and the current of the air is usually stronger and more bracing.

Physiological Action

On entering the water, under ordinary conditions, a sense of cold is felt; the skin becomes pale and roughened (goose-flesh), the circulation depressed, and the respiration more or less spasmodic; but in suitable subjects this temporary depression is quickly followed by reaction - the skin reddens, the pulse rises and becomes more forcible, while exhilaration and a sense of increased vigor indicate the stimulation of the nervous system. If the bather avoid overtaxing his powers, and will leave the bath before this period of stimulation is passed, he will probably retain, for several hours, a feeling of improved health and general well-being, and it is to such cases that the following statement of physiological results will apply.

Tissue-change is promoted, as shown by an increased excretion of urea and sulphuric acid (Beneke); not that these are immediately or inordinately increased, but the natural healthy maximum is kept up for a much longer time than usual (Ringer). Appetite and digestion are certainly promoted; but if only such a measured amount of food be taken as suffices to maintain the body-weight at a fixed point under ordinary circumstances, loss of weight is experienced owing to the increased tissue-change, while if the quantity of food be increased in proportion to the improved appetite and digestion, the body-weight is decidedly increased by a course of sea-bathing.

The skin-secretion, though at first checked, is afterward promoted: the effect of the first contraction of the skin capillaries is sometimes, if the water be very cold, to determine blood to internal organs, and hence some congestion of the kidneys may occur, and a trace of albumen may be found in the urine; but this condition soon passes off, and the albumen does not persist after the bath.

The urinary water is increased at the time, though it is said that the day's total is rather less than normal. The intestinal excretion is usually lessened, but sometimes increased (Beneke), and either constipation or diarrhoea may be induced.

Restlessness and sleeplessness are more serious symptoms occasionally caused, but in my experience as much by a residence on the sea-level as by simple bathing. The hot, strongly saline baths, as at Droitwich, do, however, often induce an extreme degree of restlessness, and should not be used too frequently.

It is worth noting that the long hair of women, when often soaked with salt-water, may fall off, but it quickly grows again.

Therapeutical Action

Sea-bathing tends to "harden the skin," to moderate undue perspiration, and to diminish the tendency to catching cold and to rheumatic attacks. It acts as a general stimulant in all conditions of constitutional debility, and also as a local stimulant, promoting absorption and improving circulation.

In Chronic Forms of Nerve-Disorder with depression, and hypochondriasis, sea-bathing is often very beneficial through a strongly stimulant action on the peripheral cutaneous nerves: by its influence on tissue-change it is said to benefit, not only in functional disorder, but even after material change in the nerve-substance (Husemann).