Your molecular machines are far too small to see. You might think that it would be impossible to affect them yourself, to speed them up or stop them, since they are so tiny and inaccessible. However, we modify the action of our own molecular machines every day. If you take a vitamin each morning, you are tuning up your molecular machines, making sure they are in top form. If your doctor gives you penicillin, you’re actively attacking the molecular machines of the bacteria in an infection. If you are unlucky and get food poisoning, a bacterium has fought back, attacking one of your molecular machines. If you take an aspirin, you are blunting the function of molecular machines in your nerves and brain. With vitamins, poisons, and drugs we deliberately modify the action of specific machines, and by careful use, we can improve their action and thus our own quality of life (Fig. 9.1).