In a chemical point of view there is no more important mineral constituent in the human body than the chloride of sodium, for it occurs nearly in every part of the system, both solid and fluid, in close and intimate relation with the organic compounds, and it materially influences their chemical and physical properties; for instance, the albumen partly owes its solubility to the presence of salt, the quantity of which causes the differences which it presents as regards its coagulation; pure caseine, which is quite insoluble, is dissolved at once on the addition of common salt; and if it is added in increased proportions it impedes the coagulation of the fibrine. Another remarkable physiological fact is that the chloride of sodium is not only uniformly present, but its various proportions are nearly definite and constant, both in the fluids and tissues; and the existence of a provision for the limitation of the quantity kept in the system causes the proportions to be little affected, in the way of excess at least, by the amount of salt the food may contain, that is, if the diet is wholesome and the individual healthy. According to Lehmann, who experimentalised on himself, the blood may contain in a normal state 4·14 parts of the chloride of sodium in 1000, and after a meal of very salty food it may be only increased to 4·15; he says it only rose to 4·18 when two ounces of salt had been taken an hour before, and two quarts of water had been drunk in the interval. The blood will not receive more than a certain amount; and as an over-amount of salt will produce extreme thirst, a quantity passes through the kidneys with the water that has been drunk; frequent drinking of course causes frequent micturition. If we take the mean of numerous observations by several experimenters, the average quantity of urine voided by healthy adult males is about 52-1/2 fluid ounces; this quantity may contain urea to the amount of 512·4 grains, chlorine 105·0 grains, and soda 125·? grains, besides other salts and extractives. If such an amount passes out with the urine we can easily account for the slight increase in the blood of Lehmann.