It is argued by those who uphold this view, that the simple forces of nature are converted by living things into the higher forces that characterize life. For instance, to keep the human body, with its wonderful will and intelligence, in health, it is necessary to feed it. The food is actually burned within the body. The heat thus obtained gives to the man both physical and intellectual vigor. It would really appear, therefore, that heat, which is a well known, simple physical force, may be converted by the animal body into other and more complex forces, or modes of motion, such as the so-called life force. [Sidenote: A certain organization characterizes life.] Naturally, should science class life as the highest or most complex of the modes of material motion, the question would arise concerning the manner in which this conversion were made possible. The answer must be that the ultimate particles of the matter composing the living thing are so arranged or organized that the great natural forces may be converted into life force. It is possible by passing heat through certain substances to make them luminous, thus converting heat into light; by employing a dynamo, mechanical energy may be converted into electrical energy; by coiling a wire around a rod of soft iron, electricity may be converted into magnetism. In short, it is well understood in science, that by the use of the right machines one form of energy may be changed into another. It is generally assumed, that the human body is so organized that the forces of heat, light and undoubtedly others, may be converted into higher forms, peculiar to living things.[A] [Footnote A: Compare, Fiske, Outlines of Cosmic Philiosophy, chap. XVI. Pearson, Grammar of Science, pp. 404-407. Dolbear, Matter, Ether and Motion, chap. XI, pp. 294-297.] [Sidenote: Protoplasm, a highly organized body, is always associated with life.] To substantiate this view, it may be recalled that the fundamental chemical individual in living thing is a very complex, unstable substance known as protoplasm. No living cell exists without the presence of this substance. It is far from being known well, as yet, but enough is known to enable science to say that it is composed of several elements, so grouped and regrouped as to transcend all present methods of research.[A] By means of this highly organized body, it is assumed that the ordinary forces of nature are worked over and made suited for the needs of the phenomena of life. [Footnote A: Pearson, Grammar of Science, p. 408.] The existence of the complex life-characteristic substance protoplasm, renders probable the view that living things, after all, differ from the rest of creation only in the kind and degree of their organization, and that life, as the word is ordinarily used, depends upon a certain kind or organization of matter,[A] which leads to a certain kind of motion. [Footnote A: Tyndall, Fragments of Science. II, chaps. IV and VI.]