If, on the other hand, the pain-lines are heaviest about the brows, the eyes, and the forehead, with only a sympathetic droop or twist of the corners of the mouth, if the nostrils are not at all distorted or too movable, if there is no fever flush and little wasting, and on turning to the eyes we find a difference between the pupils, or a wide distention or pin-point-like contraction of both or a slight squint, the picture of brain tumor would rise in the mind. Once started upon any one of these clews, then a hundred other data would be quickly looked for and asked after, and ultimately, assisted by a thorough and exhaustive examination with the instruments of precision and the tests in the laboratory, a conclusion is arrived at. This, of course, is but the roughest and crudest outline suggestive of the method of procedure. Probably not more than once in three times will the first clew that we start on prove to be the right one; but the moment that we find this barred, we take up the next most probable, and in this manner hit upon the true scent. As to the cause and rationale of these pain-lines, only the barest outlines can be given. Take the mouth for an example. When all is going well in the alimentary canal, without pain, without hunger, and both absorption of food and elimination of waste are proceeding normally, the tissues about the mouth, like those of the rest of the body, are apt to be plump and full; the muscles which open the aperture, having fulfilled their duty and received their regular wages, are quietly at rest; those that close the opening, having neither anticipation of an early call for the admission of necessary nutriment, nor an instinctive desire to shut out anything that may be indigestible or undesirable, are now in their normal condition of peaceful, moderate contraction; the face has a comfortable, well-fed, wholesome look. On the other hand, let the digestive juices fail to do their duty properly, or the swarms of bacteria pets which we keep in our food-canals get beyond control; or if for any other reason the tissues be kept from getting their proper supply of nourishment from the food-canal, the state of affairs is quickly revealed in the mouth mirror. Those muscles which open the mouth, instead of resting peacefully in the consciousness of duty well done, are in a state of perpetual fidget, twitching, pulling, wondering whether they ought not to open the portal for the entrance of new supplies of material, since the tissues are crying for food.