The quantity of the chloride of sodium in the blood is liable to great variation in different diseases; and there can be little doubt that this variation is closely connected (though whether in the relation of cause or in that of effect, we are not exactly entitled to surmise) with the histological and other transformations of the component parts of the blood. The proportions of salt greatly differ in several tissues, and also at different periods of the development of the same tissue. “Thus in muscle,” according to Enderlin, “100 parts of the ash left after incineration of ox-flesh yielded nearly 46 per cent. of the chloride of sodium and potassium; which, as this ash constitutes 4·23 per cent. of the dried flesh, would give 1·94 as the proportion of the chloride of sodium in 100 parts of the latter; and reckoning this dried residue to constitute 28 per cent. of the whole substance of the muscle (the remaining 77 parts being water) the proportion of chloride of sodium in the latter will be 0·44. These figures, as will be presently seen, bear a remarkably close correspondence to those which represent the proportion of chloride of sodium in the ash, solid residue and entire mass of the blood.”[57] Next to muscle, cartilage contains the largest amount of the chloride of sodium, and this especially in the temporary cartilages of the fœtus, its place being taken by the phosphate of lime as it approaches the time of birth. The percentage of the chloride of sodium contained in the ash of the costal cartilage of an adult is about 8·2; in the laryngeal cartilage 11·2; but as the ash does not constitute above 3·4 per cent. of the entire substance the percentage of the chloride of sodium in the latter is, at the most, 0·38 of the whole, or less than that of blood and muscle. Only from 0·7 to 1·5 per cent. could be extracted from the ash of bone. Besides the important uses of the chloride of sodium in the blood to which we have already adverted, it serves the purpose of furnishing the hydrochloric acid required (by many animals, at least) for the gastric secretion; and it likewise supplies the soda-base for the alkaline phosphate, whose presence in the blood appears to serve a most important purpose in the respiratory process. Moreover, there is reason to think, from the experiments of Boussingault upon animals, as well as from other considerations, that the presence of salt in the blood and excreted fluids facilitates the deportation of excrementitious substances from the blood. The proportion in which it occurs in the principal animal fluids is represented by the following table, constructed by Lehmann chiefly from his own analyses; it is highly interesting, and shows us at a glance that it is more important in the economy than any other substance, and is significant of the fact that health cannot exist long if the chloride of sodium is below the normal amount.