Work means waste, equally to a human body and a locomotive engine. "More work more waste," is a motto alike true of the mechanic's apparatus and of the mechanic himself. Not an action, we repeat, is performed by us which is not accompanied by an expenditure of force derived from and accompanied by a proportional waste of substance. The movements of the muscles, the beating of the heart, the winking of an eyelid, the thinking a thought, entail wear and tear upon the muscles that work and the brain-cells that think. Every action necessitates bodily waste and corresponding physical repair. Waste, however, cannot of necessity be a single and final process in a living body, unless, indeed, we were born with a full complement of matter, and were permitted in the order of nature to live on the principal with which we had been provided, instead of wisely using that principal as a means of gaining a livelihood through the interest it acquired. That we are not so constituted is an evident fact, hence our bodies demand pretty constant repair as a companion action to that of work, labor, and duty. This process of repair consists in the reception of matter from the outer world, in the transformation of this matter into ourselves, and in its utilization in the work and repair of the frame. Such matter we shortly name food, and the processes whereby it is converted into our own bodily substance we term digestion.