Relative prevalence in man and animals. Causes of difference. Kidneys as eliminating organs for nitrogenous material, toxins, bacteria, mineral, vegetable and animal poisons, diuretic drinking water, condition powders, cantharides, urea, etc. Suppression of urine, precipitation of urine. Filtration through kidney. Secretion. Urinary solids. Nervous control of secretion. Excess. Diseases of the urinary organs are less prevalent in the lower animals than in man, owing largely no doubt to the greater simplicity of their habits of life and to the comparative shortness of the lives of those that are kept for meat producing. It is a mistake, however, to suppose that they are so infrequent as would appear, since the absence of subjective symptoms in the animal allows a number of the milder forms of renal disease to be passed over without recognition. In man the excessive consumption of animal food, the lack of exercise, the abuse of alcohol, the prevalence of venereal diseases, conduce largely to renal troubles, while animals in general escape. Yet animals suffer much more extensively than is generally supposed. The kidneys are, as in man, the eliminating organs for superfluous and waste nitrogenous matter, and in overfed animals may be overcharged with this work. They are the general emunctories for the soluble poisonous products of bacteria and plants, which may stimulate the urinary secretion, and from these irritation may result. It is through the kidneys that the bacteria themselves largely leave the animal body, and trouble is liable to come during their passage. Further, exposure to cold tends to =increase the urinary secretion=, over-stimulating the kidneys, and the same may come from diuretic drinking waters and condition powders, also from cantharides and other diuretic agents applied to the skin. Urea and many toxins are diuretic, hence the occurrence of polyuria at and after the crisis of fevers. On the other hand =suppression of the urinary secretion= may occur in connection with profuse perspirations in hot weather, with prolonged diarrhœa, or with privation of water, and in such cases the liquid becomes concentrated and irritating and there is a disposition to precipitate its solids under slight disturbing causes. As conducive to such precipitation may be named foreign solid bodies, bacterial ferments and probably the goitre poison since gravel and calculus are common in goitrous regions. There are two forms of elimination through the kidneys. 1, _filtration_; 2, _secretion_. 1. _Filtration_ is referred to the glomeruli, and is determined by the relative blood pressure. Increase of pressure causes increase of watery transudation. Digitalis increases heart action and arterial pressure, and accidently urination. Excessive consumption of water and watery liquids increases intravascular tension, and the amount of urine.