It is remarkable how many of our disease-enemies appear to have a preference for the lung as a point of attack. In the language of _Old Man Means_ in "The Hoosier Schoolmaster," the lung is "their fav'rit holt." Our deadliest diseases are lung diseases, headed by consumption, seconded by pneumonia, and followed by bronchitis, asthma, etc.; together, they manage to account for one-fourth to one-third of all the deaths that occur in a community, young or old. No other great organ or system of the body is responsible for more than half such a mortality. Now this bad eminence has long been a puzzle, since, foul as is the air or irritating as is the gas or dust that we may breathe into our lungs, they cannot compare for a moment with the awful concoctions in the shape of food which are loaded into our stomachs. Even from the point of view of infections, food is at least as likely to be contaminated with disease-germs as air is. Yet there is no disease or combination of diseases of the whole food canal which has half the mortality of consumption alone, in civilized communities, while in the Orient the pneumonic form of the plague is a greater scourge than cholera. It has even been suggested that there may possibly be a historic or ancestral reason for this weakness to attack, and one dating clear back to the days of the mud-fish. It is pointed out that the lung is the last of our great organs to develop, inasmuch as over half of our family tree is under water. When our mud-loving ancestor, the lung-fish (who was probably "one of three brothers" who came over in the Mayflower--the records have not been kept) began to crawl out on the tide-flats, he had every organ that he needed for land-life in excellent working condition and a fair degree of complexity: brain, stomach, heart, liver, kidneys; but he had to manufacture a lung, which he proceeded to do out of an old swim-bladder. This, of course, was several years ago. But the lung has not quite caught up yet. The two or three million year lead of the other organs was too much to be overcome all at once. So carelessly and hastily was this impromptu lung rigged up that it was allowed to open from the front of the gullet or [oe]sophagus, instead of the back, while the upper part of the mouth was cut off for its intake tube, as we have already seen in considering adenoids, thus making every mouthful swallowed cut right across the air-passages, which had to be provided with a special valve-trap (the epiglottis) to prevent food from falling into the lungs.