If the efficacy of a natural mineral water depended solely on its watery constituent I do not for one moment think that the resort of sufferers to the various natural springs would have successfully stood the test of centuries, as it undoubtedly has. The fact is that in judging of the effect of natural mineral waters we have been too much under the domination of analytical chemistry, and that our deductions from these results have been consequently biased and cramped. The more I consider the therapeutic effects of the natural mineral waters the more convinced I am that chemical analysis, although it can inform us what are the mineral constituents of the natural waters, is yet unable to determine exactly the state of the salts dissolved in them. The "ionic or electrical dissociation theory " and the existence of the mineral constituents of natural waters as " ions " are leading our thoughts to a new and, I believe, correct appreciation of the therapeutic values of these waters.

An element or a group of elements divorced from the rest of the original molecule is an " ion." According to the ionic theory metallic salts in very dilute solutions are completely split up into their "ions" so that all the properties of these solutions must be the sum of the properties of the separate "ions." In concentrated solutions much of the salt remains in the undisso-ciated state and only a small proportion in the form of dissociated " ions," whereas in most of the natural mineral waters, which are weak solutions of salts, the mineral constituents are mainly, if not entirely in many waters, in the form of " ions," and in this form the therapeutic effects and potency may be quite different from those of the undissociated salts. Ionic dissociation does not, therefore, alter the percentage composition of a salt, but may very materially alter its therapeutic properties, so that in all probability the "ions" rather than the salts are responsible in great part for the effects of mineral waters.

In intimate relation with this aspect of the matter is the question of radio-activity in hydrotherapy. Our conception of the atom as an indivisible and finite body is disappearing, and, in view of the recent discoveries that have been made in connexion with radio-activity, the atom must be conceived as consisting of an aggregate of corpuscles, and each atom has associated with it a definite charge of electricity, such an electrically charged atom being an " ion." The smallest unit of electric charge is known as an " electron " and the atom is charged with a number of these electrons, which are in a state of vigorous motion among themselves within the atom. Radio-activity consists in the flinging away with great violence of actual atoms. The substance left is also radio-active, and ultimately one of the residues seems to discharge electrons instead of atoms of matter, thus effecting a transmutation of matter.

Now, most, if not all, of the natural mineral waters which have been examined have been found to be distinctly radioactive, and the lower the mineralization of the water, the more intense is its radio-activity. In this, I think, lies the explanation of the fact that an artificially prepared mineral water, although it may be made identical in chemical composition with the natural one, does not possess the same therapeutic effects as the natural water, since it is lacking, at all events to any extent, in the property of radio-activity. A natural water at the moment of its discharge from the earth is radio-active, whereas an ordinary drinking water does not possess this property to any appreciable extent. Hence also the desirability of drinking the water at its source, since by the bottling and keeping of a natural water the radio-activity is to a great extent lost. When we consider the marked influence of radio-active emanations on new growths and various morbid tissues, is it too remarkable to conceive that a radio-active mineral water will exercise a potent effect on those morbid changes within the body which are connected with abnormal tissue metabolism?