The environmental conditions of the life of cells in a complex animal are too complicated for an elemental study; the elements of lire and its basic necessities are bet- ter understood in a simple organism, or in a one-celled animal; but for purposes of description, it is most con- venient to speak of the properties of mere protoplasm. AIl the vital needs of the most highly organized animal are .pr.esent in any part of the protoplasmic substance of which ?t ,s composed. Protoplasm is a chemical substance, or group of sub- stances, the structure of which is very comp]ex but is main- tained so long as there is no disturbance in the environ-
'??°- °?? BCIs ?BCIs ?BC]s A ]3 C FIG. 6?. Diagram show]ng the relation of the germ ce]ls (GCIs) and the body cells (BCIs) in successive generations A fertilized germ cell of generation A forms the germ cells and b?y cells of B, a fert]lized germ cell of B forms the germ cells and b?y cells of C, and so on. The offspring C of B derives nothing from the body cells of the parent B, but both offsp6ng C and parent B have a oemmon origin in a germ cell of A
metat. Let some least thing happen, however, such as a change in the temperature, in the strength of the light, in the weight of pressure, or in the chemical composition of the surrounding medium, and the protoplasmic molecules, in the presence ofoxygen, are likely to have the balance of their constituent particles upset, whereupon they partly decompose by the union of their less stable elements with oxygen to form simpler and more permanent compounds. The decomposition of the protoplasmic substances, like all processes of decomposition, liberates a certain amount of energy that had been stored in the making of the molecule, and this energy may manifest itselfin various ways. Ifit
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