There lie before me the “Letters on Chemistry” of an illustrious German chemist.[36] They contain the expression of the latest scientific results hitherto attained. Whatever view those who follow us may adopt, we must in the meantime accept, to a certain extent, of those contained in these “Letters.” A phenomenon must be accepted as a fact until refuted by another; and the last experiment, until refuted, expresses the nearest approach to that truth which, up to the moment, man had been able to attain. Simple observation tells man many truths. It shows him that out of grass, herbivora, or grass-eating animals of all kinds--from the timid hare to the swift and powerful horse--from the fierce buffalo to the sagacious and irresistible elephant--find the means for forming muscle and bones, viscera and skin. Out of a similar food man himself, though no doubt omnivorous, can also derive the means of support. The rice-eating population of India are not deficient in energy; whilst it is equally certain, though less surprising, no doubt, that out of that which once was a living animal, man and the carnivora derive a considerable part of their subsistence. [36] “Letters on Chemistry.” By Justus von Liebig. London, 1857. No experiments can set aside these simple views, which indeed form the basis of all inquiry; but civilized man, as I have shown, appeals to the soil mainly for support. He trusts to the cerealia, and to those exuberant and abundant crops of legumina and of grains required for the support of herds of animals, which the uncultivated field could never maintain. Hence arose agriculture, the most useful of all the practical arts--not yet a science, but likely in time to become one. Chemists assert--and I see no reason to doubt their experiments--that the ash of the blood of graminivorous animals is identical with that of the ash of grain; the incombustible constituents of the blood of men, and of such animals as consume a mixed food, are the constituents of the ashes of bread, flesh, and vegetables; the carnivorous animal contains in its blood the constituents of the ash of flesh.[37] All these substances ought to be found in grass alone. [37] Liebig, p. 384.