The ultra-violet rays are said to have a very beneficial effect upon the teeth. Experiments carried out in Paris, using a mercury vapour lamp as the source of light, show that discoloured teeth are whitened and given a pearly lustre by these rays, at the same time being sterilized so that they do not easily decay. The Röntgen rays are used for the treatment of lupus, and more particularly for deeper growths, such as tumours and cancers, for which the Finsen rays are useless, owing to their lack of penetrating power. The action of these two kinds of rays appears to be similar, but the X-rays are much the more active of the two. Electricity is often applied to the body through water, in the form of the hydro-electric bath, and such baths are used in the treatment of different kinds of paralysis. Electric currents are used too for conveying drugs into the tissues of the body. This is done when it is desired to concentrate the drug at some particular point, and it has been found that chemicals can be forced into the tissues for a considerable distance. Dr. Nagelschmidt, a great authority on medical electricity, has suggested the use of electricity for weight reducing. In the ordinary way superfluous flesh is got rid of by a starvation diet coupled with exercise, but in many cases excessively stout people are troubled with heart disorders and asthma, so that it is almost impossible for them to undergo the necessary muscular exertion. By the application of electric currents, however, the beneficial effects of the gentle exercise may be produced without any exertion on the part of the patient, and an hour’s treatment is said to result in a decrease in weight of from 200 to 800 grammes, or roughly 7 to 27 ounces. CHAPTER XXVI OZONE The great difference between the atmospheric conditions before and after a thunderstorm must have been noticed by everybody. Before the storm the air feels lifeless. It does not satisfy us as we draw it into our lungs, and however deeply we breathe, we feel that something is lacking. After the storm the air is delightful to inhale, and it refreshes us with every breath. This remarkable transformation is brought about to a very large extent by ozone produced by the lightning discharges.