Cold foot-baths should not be used by very old people, as they distend the brain-vessels which, as a rule, are altered in such people and may more easily rupture; if taken, a wet, cold towel should be wound round the head. Cold baths generally are often beneficial in the case of certain nervous troubles, such as neurasthenia and hysteria; only they must never be too cold nor too prolonged, as otherwise the effects may be very depressing. A short cold friction of the body every morning on rising is of great advantage in the preservation of health. In kidney trouble we must, however, be careful, as often an increase of albuminuria has been observed after them. Sea baths are especially refreshing, owing to the sodium content of the salt water. Our own observations teach us that a bath had best be taken by first using water of the highest temperature that can be borne (about 42 degrees C.). Those who can stand it might continue to add hot water until the skin is quite red. Abundant perspiration will then appear on the head, face, and neck. After having perspired freely, we should then allow cold water to enter until the bath has become cool. It usually takes some time to cool the water off thus gradually, but after such a bath there is a feeling of great exhilaration, especially after warm sea baths taken in this manner. We consider that hot baths of long duration—say 30 to 45 minutes—are especially useful in cases of kidney disease, or as a preventive of such. We could take them twice a week as a means of eliminating the toxic products of metabolism, but _it is an essential condition that the heart and blood-vessels be in good condition_. The Japanese are in the habit of taking such hot baths at an enormously high temperature, and they feel the better for it. Bathing generally is favorable not only to the kidneys, but to all the organs, as the processes of oxidation are thereby promoted, and our prospects for long youth and long life are bettered. ------------------------------------------------------------------------ CHAPTER XXVII. HYGIENE OF THE SKIN AND KIDNEYS BY MEANS OF PERSPIRATION. UNDER normal conditions we daily lose a certain amount of water and also of gaseous and solid products, among them many harmful ones, through the invisible and insensible perspiration of the skin. That such a process does actually take place is proved by our personal observation and by the disagreeable feeling produced in cold and damp weather by the checking of such perspiration. We can even be seriously affected if by disease or by extensive burns a large portion of the skin be destroyed, thus abolishing this insensible perspiration.