That poisonous products coming from the intestinal tube are apt to produce even serious changes in the kidneys has been proved by Heller and Fishel after catarrhs of the stomach and intestines. At the same time we will also mention that in cases of intestinal auto-intoxication we can also observe a diminution in the quantity of urine, as noted by several authors, of whom we specially mention Boas and Hemmeter.[224] Footnote 224: Hemmeter: Loc. cit. From the foregoing there can be no doubt that most of the toxic products in the blood are eliminated by the kidneys. This is also the manner in which the nitrogenous end-products of metabolism leave the body. The kidneys act as a kind of filter for these products. When the kidneys, however, are changed or degenerated by the formation of connective tissue and loss of the elements of excretion, as in old age, then these products will be retained in a greater or smaller number, and a condition of auto-intoxication follows, to which we have previously ascribed a great rôle in the pathology of old age. Logically, if we wish to prevent old age coming on too soon, or a diminution of our chances for a long life, we must do our best to prevent such a diseased condition. ------------------------------------------------------------------------ CHAPTER XXII. HYGIENE OF THE KIDNEYS, AND THE PREVENTION OF RENAL DISEASE. THE most rational hygiene of the kidneys for the prevention of kidney diseases consists in the avoidance of all those causes which are injurious to the kidneys, and which we have mentioned in the previous chapter. A great part of the poisonous products that are eliminated by the kidneys are introduced with the food and beverages, and it is important for us to bear in mind the fact that what we eat or drink must pass through our kidneys, and that the structure of these organs is delicate; that the most important secreting parts are composed of fine epithelium which can easily be desquamated by the passage of irritating products. Thus we note the appearance of hyaline casts after different kinds of spices and stimulating liquors, especially if taken in large quantities.