Our bodies, therefore, are part of the material universe, and subject to the laws or ways of being of this universe. The first of these laws that we know is the law of causation. Every change in the universe has its cause, and that in turn had another cause; this chain is never broken, no matter how far we go, and the same causes universally produce the same effects. If you see a ball move on a billiard table, you know that the ball did not move itself; you know that something struck the ball or tilted the table. You discover that the motion of the ball moves the air around it, and the waves of that motion are spread through the room. They strike the walls, and the motion is carried on through the walls, and if we had instruments sensitive enough, we could feel the motion of that billiard ball at the other side of the world, and a few million years from now at the most remote of the stars. This is what is called the law of the conservation of energy, and when we discover something like radium which seems to violate that law by giving out unlimited quantities of energy, we investigate and discover a new form of energy locked up in the atom. In the disintegration of the atom we have a source of power which, when we have learned to use it, will multiply perhaps millions of times the powers we are now able to use on this earth. But energy, no matter how many times it is transformed, and in what strange ways it reappears, always remains, and is never destroyed, and never created out of nothing. My friend the great physiologist once took me into his laboratory and showed me a little aquarium in which some minute creatures were wiggling about--young sea-urchins, if I remember. The physiologist took a bottle containing some chemical, and dropped a single drop into the water, and instantly all these little black creatures, which had been darting aimlessly in every direction through the water, turned and swam all in one direction, toward the light. They swam until they touched the walls of the aquarium, and there they stuck, trying their best to swim farther. "And now," said my friend, "that is what we call a 'tropism,' and all life is a tropism. What you see in that aquarium means that some day we shall know just what combination of chemicals causes a human being to move this way or that, to do this thing or that. When bio-chemistry has progressed sufficiently, we shall be able to make human qualities, perhaps in the sperm, perhaps in the embryo, perhaps day by day by means of diet or injection." Said I: "Some day, when bio-chemistry has progressed far enough, you will know what combination of chemicals causes a man to vote the Democratic or Republican ticket." "Why not?" answered my friend. (He has a sense of humor about all things except this sacred bio-chemistry.)