Said I: "When you have got to that stage, keep the secret carefully, and we will fix up a scheme, and a few days before election we will release some gas in our big cities, and sweep the country for the Socialist ticket." But jesting aside: if the human body is a material thing, existing in the material world and subject to causation, there must be material reasons for the actions of human bodies, just the same as for the moving of billiard balls. We hear the sound of a billiard ball striking the cushion, and we are prepared to accept the idea that the thing we call hearing in us is caused by the impinging of sound waves upon our eardrums. And if we investigate human beings in the mass, we find every reason to believe that they act according to laws, and that there are material causes for their acts. If you get up and shout fire in a theater, you know how the audience will behave. If you study statistics, you can say that in any large city a certain fixed number of human beings are going to commit suicide every month; you can even say that more are going to commit suicide in the month of June than in any other month. You can say that more people are going to die at two o'clock in the morning than at any other hour. You know that certain changes in the weather will cause all human beings to behave in the same way. You know that an increase of prices or an increase of unemployment will cause a certain additional number of men to commit crimes, and a certain additional number of women to become prostitutes. You know that if a man overeats, his thoughts will change their color; he will have what he calls "the blues." I might cite a thousand other illustrations to prove that human minds are subject to material laws, and therefore to investigation by the bio-chemists. But now, stop a moment. Here you sit reading a book. Something in the book pleases you, and you say, "Good!" Perhaps you slap your knee or clench your fist. Now here is a motion of your hand, which stirs the air about you, and which, according to the laws of energy, will spread its effects to the other side of the world, and even to the farthest of the stars. Or perhaps the book makes you angry, and you throw it down in disgust; an entirely different motion, which will affect the other side of the world and the farthest of the stars in an entirely different way. The machine of the universe will be forever altered because of that slapping of your knee or that throwing down of your book.