Now, my good friend, your living body, and my own, are laboratories, in which changes of precisely the same kind are constantly brought about; your living body, and my own, are made of an enormous quantity of separate chambers and vessels, very small, it is true, but nevertheless such as can be seen quite distinctly when they are looked for with the microscope. In these small chambers and vessels different kinds of substances are thrown together, exactly as the zinc, and acid, and blue vitriol are in the laboratory-chambers of the electric telegraph. The chambers and vessels of the living laboratory lie between meshes of the supply pipes of the body, and it is indeed their minute cavities which are drenched by the circulating streams of the dissolved food (see “Value of Good Food”), and in which that dissolved food gets to be transformed into flesh and fat, gristle and bone, tendons and skin, fibres and nerves. The blood, which is pumped forth with such vigor from the heart, creeps along slowly through the smallest and furthest branches of the supply-pipes, in order that plenty of time may be given for all these changes to be worked out in the chambers of the frame. But the fibres and skin, the flesh and the nerves, when they have been built up, are also changed into waste substance by admixture with yet other ingredients which the blood brings to the little chambers. In the cavities of the living laboratory, as in those of the electric telegraph, these changes of substance lead to the setting free of agents before concealed, which agents then operate in the production of movements and of other living effects. When I now raise my arm up above my head, I am able to do so because some of the flesh of which my arm is composed, is changed into another kind of substance, the moving power being set free during the change. When I feel this hard stone which I take up in my hand, I am able to do so because some of the substance of which my body is made, is changed into another kind of material at the instant that I feel. This, then, is how strength comes out of food. The food is changed into flesh, and the flesh is converted into two distinct parts, waste substance and moving and living power. The power was originally concealed in the food, placed there by the provident hand of the Divine Author of Nature, in order that it might be forthcoming for this useful service when it was required. In simple words, material substance is destroyed in order that power may be extracted from it. Material substance, in living bodies, is turned into power. This is the mechanism by which God works in these, the most wonderful of the productions of his hands.