"Perhaps not; but if you think my criticisms harsh and uncalled for, let us get down to cold facts. Did it ever occur to you how very few people live to be even one hundred and twenty-five years old? You surely will admit that there is no reason why a man should not live to that age, barring accidents. We know that in Bible times there were lots of old fellows who passed their three hundredth birthday, and a chap named Methuselah claimed to be nine hundred and ninety-nine years old." "Nine hundred and sixty-nine, was it not?" I asked. "Perhaps you are right, but sixty-nine or ninety-nine, I am inclined to be a little sceptical about that record myself; there is one thing in its favor, however, and that is, that he made it an even nine hundred and ninety-nine, and not one thousand. Of course, you know there are plenty of people living to-day who are over one hundred years old, and some who have reached the very satisfactory age of one hundred and twenty-five; most of them, however, live in Bulgaria, Mexico, or some out-of-the-way place, and are so poor that they have to live abstemiously." "Then you consider the secret of longevity to be a matter of diet?" said I. "Partly that, and partly proper care of the nervous system; but come downstairs, and let us have a cigarette; I am dying for a smoke." We floated down to the office, which happened to be unoccupied at the time. The medical ghost helped himself to a cigarette from a trayful on the mantel-piece, and lighting it, he seated himself in an armchair, and puffed away with evident enjoyment. I noticed the smoke, which he inhaled continually, oozed from all parts of his body. [Illustration: THE SMOKE CONTINUALLY OOZED FROM ALL PARTS OF HIS BODY.] "My dear fellow," he said impressively, "you must understand that all diseases are caused by germs--microscopic bugs and plants, you know, many of them so small that they are invisible to an ordinary microscope, or, if seen at all, are not recognized. There are thousands and thousands of them, and each and every one has its mission in life, and preys upon and destroys other germs. Now, the human body is constantly getting a lot of germs inside of it which do not belong there. Some are taken in by the lungs, while floating in the air; some by the stomach, by the food and drink; some by the skin, etc. "These germs are met by their natural enemies which live in man's blood--his body-guard, as it were--and are destroyed. But if the attacking army is very large, or from some reason the home army has been weakened and decimated, then the invaders flourish, establish themselves and wax powerful and strong, and the man becomes what is called 'sick.' "Come," he said, rising abruptly, and throwing the unconsumed end of his cigarette into the fireplace. "Come with me to the laboratory, and I will show you in about two minutes more than I could explain if I talked for years, and a great deal more satisfactorily."