The direction in which medicine is chiefly working at the present time is that of introducing into the body one disease with the idea of excluding other diseases. It is conceived that cow-pox is antagonistic to small-pox, erysipelas possibly to cancer, and so on. All the talk in medical circles is of serum and attenuated virus. And, apart from animal products administered by injection, we cure or attempt to cure all diseases by administering poisons--animal, vegetable or mineral. Just as by antiseptics we poison the germ which causes festering and inflammation, so by drugs we attempt to poison disease--for all drugs are practically poisons. The principle of their administration is almost wholly empirical. If you ask a doctor why phenacetin reduces fever, it is impossible to get beyond a metaphysical explanation. He will reply that phenacetin reduces fever by lowering the blood pressure, or something of that kind. But this merely re-states the problem. Why does phenacetin lower blood pressure? We do not know. The substitution of asepsis for antisepsis--that is, of cleanliness for disinfection--has hardly yet been perceived to be in a certain sense the greatest advance in therapeutics since Hippocrates. It probably contains the germ of future medical treatment. Hereafter we shall not try to cast out devils of disease by other disease-germs only less devilish. We shall learn enough of the causes of disease to stop them at their source, and knowledge growing from more to more, which has taught us exactly how "matter in the wrong place"--of whatever sort--is the source of all disease, will also show how matter may generally be kept in its right place.