The Nutritive Apparatus.--This consists of organs for the purpose of taking in food or nourishment, digesting it, and distributing it throughout the body wherever it is needed. These are chiefly the mouth and teeth for receiving and chewing the food, the stomach and intestines for digesting and absorbing it, and the heart and blood-vessels for distributing it to the body. The Moving Apparatus.--For the purpose of producing motion, we have the muscles and the bones, by which the food is received, masticated, and swallowed, the blood circulated, the body moved about from place to place, and speech, expression, respiration, and many other important functions performed. The Thinking and Feeling Apparatus.--The brain and nerves afford the means of thinking and feeling, also giving rise to all the activities of the body by the production of nerve force. To aid the brain and nerves, we have special organs provided, termed the organs of special sense; as the eye for sight, the ear for hearing, the nose for the detection of odors, the tongue for tasting, the skin and the mucous membrane for the sense of touch. The Purifying Apparatus.--Waste matter accumulates in the body so rapidly that it is necessary to have abundant and efficient means to remove the same, and prevent death by obstruction. This work is performed by the lungs, liver, kidneys, skin, and mucous membrane. Each organ and tissue possesses the power to repair itself. Animal heat, which is also necessary to life, is not produced by any special set of organs, but results incidentally from the various other processes named. The Reproductive Apparatus.--As there is a stomach to digest, a brain to think, a pair of lungs to breathe, etc., so there are special organs for reproducing the species or producing new individuals. These organs have been carefully described in the preceding portion of this volume, so that we do not need to repeat the description here. Unlike all the other organs of the body, they are intended for use only after full development or manhood has been attained; consequently, they are only partially developed in childhood, becoming perfected as the person becomes older, especially after about the age of fourteen to eighteen, when puberty occurs. The lungs, the stomach, the muscles, and other organs must be used constantly from the earliest period of infancy, hence they are developed sufficiently for efficient use at birth. The fact that the sexual or reproductive organs are only fully developed later on in life, is sufficient evidence that they are intended for use only when the body has become fully mature and well developed.