Licence: Public Domain Mark
Credit: Health lectures for the people. Source: Wellcome Collection.
Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.
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![wMch the human body differs from the engine in connection with its supply of matter and energy. In the engine the coal which is shovelled into the furnace burns there, gives off its energy for the production of mechanical work in the engine, but has never any further connection with the machine. Supply the engine with coal, it will produce work ; cut off the supply of coal, no work will be performed. With the human body, on the other hand, if the supply of food be cut off, the body will still go on doing work. It will use its own substance as a source of energy. COMPOSITIOX OF BODY. Of what is the body composed 1 We may roughly divide the substances composing the body into living and dead matter. LIVING AND NON-LIVING STRUCTURES DEAD PARTS OF BODY. For all practical purposes our outer skin, our bones, our liga- ments, our teeth, hair, and nails, may be considered as dead. They have been formed during our growth, and are retained simply for the support and binding together of the body. They may be looked upon as the hull and spars of a ship, while the living parts of the body may be looked upon as the crew. CHIEF LIVING PART OF BODY. The chief of the ]i\ing parts of the body is the /lesh or muscle, through the activity of which we are able to move about—which, in fact, acts upon the ligaments and bones, much as the crew act upon the rigging of the ship. We have also the nervous structures of the body which govern the muscles, and which might be compared to the officers com- manding our imaginary ship. A certain amount of living tissue, too, has for its duty, as we have already seen, the preparation of the necessary food for the muscles and nerves. And the food so prepared when in excess of the demands of the muscles and nerves is stored up as fats and as a form of starch. IMPORTANCE OF MUSCLE. The muscle is the great work producer. It constitutes no less than 42 or 43 per cent, of substance of body.](https://iiif.wellcomecollection.org/image/b21057631_0082.jp2/full/800%2C/0/default.jpg)
