226. But with all this, we do not pretend to have discovered the true nature of life itself, or even the true nature of its relation to the material universe. What we have ventured is the assertion that, as far as we can judge, life is always associated with machinery of a certain kind, in virtue of which an extremely delicate directive touch is ultimately magnified into a very considerable transmutation of energy. Indeed, we can hardly imagine the freedom of motion implied in life to exist apart from machinery possessed of very great delicacy of construction. In fine, we have not succeeded in solving the problem as to the true nature of life, but have only driven the difficulty into a borderland of thick darkness, into which the light of knowledge has not yet been able to penetrate. _Organized Tissues are subject to Decay._ 227. We have thus learned two things, for, in the first place, we have learned that life is associated with delicacy of construction, and in the next (Art. 220), that delicacy of construction implies an unstable arrangement of natural forces. We have now to remark that the particular force which is thus used by living beings is chemical affinity. Our bodies are, in truth, examples of an unstable arrangement of chemical forces, and the materials which composed them, if not liable to sudden explosion, like fulminating powder, are yet preeminently the subjects of decay. 228. Now, this is more than a mere general statement; it is a truth that admits of degrees, and in virtue of which those parts of our bodies which have, during life, the noblest and most delicate office to perform, are the very first to perish when life is extinct. “Oh! o’er the eye death most exerts his might, And hurls the spirit from her throne of light; Sinks those blue orbs in their long last eclipse, But spares us yet the charm around the lips.” So speaks the poet, and we have here an aspect of things in which the lament of the poet becomes the true interpretation of nature. _Difference between Animals and Inanimate Machines._ 229. We are now able to recognize the difference between the relations to energy of a living being, such as man, and a machine, such as a steam-engine. There are many points in common between the two. Both require to be fed, and in both there is the transmutation of the energy of chemical separation implied in fuel and food into that of heat and visible motion. But while the one--the engine--requires for its maintenance only carbon, or some other variety of chemical separation, the other--the living being--demands to be supplied with organized tissue. In fact, that delicacy of construction which is so essential to our well-being, is not something which we can elaborate internally in our own frames--all that we can do is to appropriate and assimilate that which comes to us from without; it is already present in the food which we eat. _Ultimate Dependence of Life upon the Sun._