Similarly, upon the physical side, because children who breathe through the mouth are apt to have a vacant expression, to be stupid and inattentive, undersized, pigeon-breasted, with short upper lip and crowded teeth, we have leaped to the conclusion that it is a fearsome and dangerous thing to breathe through your mouth. All sorts of stories are told about the dangerousness of breathing frosty air directly into the lungs. Invalids shut themselves scrupulously indoors for weeks and even months at a stretch, for fear of the terrible results of a "blast of raw air" striking into their bronchial tubes. All sorts of absurd instruments of torture, in the form of "respirators" to tie over the mouth and nose and "keep out the fog," are invented, and those who have the slightest tendency to bronchial or lung disturbances are warned upon pain of their life to wrap up their mouths whenever they go out-of-doors. As a matter of fact, there is exceedingly little evidence to show that pure, fresh, open air at any reasonable temperature and humidity ever did harm when inhaled directly into the lungs. In fact, a considerable proportion of us, when swinging along at a lively gait on the country roads, or playing tennis or football, or engaged in any form of active sport, will be found to keep our lips parted and to inhale from a sixth to a third of our breath in this way, and with no injurious results whatever. Nine-tenths of all the maladies believed to be due to breathing even the coldest and rawest of air are now known to be due to invading germs. Nevertheless, mouth-breathing in all ages has been regarded as a bad habit, and with good reason. It was only about thirty years ago that we began to find out why. A Danish throat surgeon, William Meyer, whose death occurred only a few months ago, discovered, in studying a number of children who were affected with mouth-breathing, that in all of them were present in the roof of the throat curious spongy growths, which blocked up the posterior opening of the nostrils. As this mass was made up of a number of smaller lobules, and the tissue appeared to be like that of a lymphatic gland, or "kernel," the name "adenoids" (gland-like) was given to them. Later they were termed _post-nasal growths_, from the fact that they lay just behind the rear opening of the nostrils; and these two names are used interchangeably. Our knowledge has spread and broadened from this starting-point, until we now know that adenoids are the chief, yes, almost the sole primary cause, not merely of mouth-breathing, but of at least two-thirds of the injurious effects which have been attributed to this habit. Mouth-breathing is not simply a bad habit, a careless trick on the part of the child. We have come to realize that physical bad habits, as well as many mental and moral ones, have a definite physical cause, and that _no child ever becomes a mouth-breather as long as he can breathe comfortably through his nose_.