As there are some twenty-four pairs of these in an area only slightly greater than that of the outspread hand, and as they are capable of acting with every imaginable grade of vigor and in every possible combination, it can readily be seen what an infinite and complicated series of expressions—or, in other words, indications of the state of affairs within those different orifices—they are capable of. Only the barest and rudest outlines of their meaning and principles of interpretation can be attempted. To put it very roughly, the main underlying principle of interpretation is that we make our first instinctive judgment of the site of the disease from noting which of the three great orifices is distorted furthest from its normal condition. Then by constructing a parallel upon the similarity or the difference of the lines about the other two openings, we get what a surveyor would call our "lines of triangulation," and by following these to their converging point can often arrive at a fairly accurate localization.
The greatest difficulty in the method, though at times our greatest help, is the extraordinary and intimate sympathy which exists between all three of these groups. If pain, no matter where located, once becomes intense enough, its manifestations will travel over the face-dial, overflowing the organ or system in which it occurs, and eyes, nostrils, and mouth will alike reveal its presence. Here, of course, is where our second great process, so well known in all clew-following, elimination, comes in.
A patient comes in with pain-lines written all over his face. To put it very roughly—has he cancer of the stomach? Pneumonia? Brain tumor? If there be no play of the muscles distending and contracting the nostrils with each expiration, no increased rapidity of breathing, no gasp when a full breath is drawn, and no deep red fever blush on the cheeks, we mentally eliminate pneumonia. The absence of these nasal signs throws us back toward cancer or some other painful affection of the alimentary canal. If the pain-lines about the mouth are of recent formation, and have not graved themselves into the furrows of the forehead above and between the eyebrows; if the color, instead of ashy, be clear and red, we throw out cancer and think of colic, ulcer, hyperacidity, or some milder form of alimentary disease.
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.
As the strongest of these are those which pull the corners of the mouth outward and downward, the resultant expression is one of depression, with downward-curving angles to the mouth. The eyes, and even the nostrils, sympathetically follow suit, and we have that countenance which, by the cartoonist's well-known trick, can be produced by the alteration of one pair of lines, those at the angles of the mouth, turning a smiling countenance into a weeping one. On the other hand, if all these processes of nutrition and absorption are proceeding as they should, they are accompanied by mild sensations of comfort which, although they no longer reach our consciousness, reveal themselves in the mouth-opening muscles, and they gently contract upward and outward, in pleasurable anticipation of the next intake, and we get the grin or the smile.
If, on the other hand, these digestive disturbances be accompanied by pain, then another shading appears on our magic mirror, and that is a curious contraction of the mouth, with distortion of the lines surrounding it, so violent in some cases as positively to whiten the lips or produce lines of paleness along the course of the muscles. This is the set or twisted mouth of agony, and is due to a curious transference and reflex on this order: that inasmuch as the last food which entered the alimentary canal seems to have caused this disturbance and pain, no more will be allowed to enter it at present under any conditions. And as our alimentary instincts are the most fundamental of all, by a due process of transference, mental agony calls into action this same set of muscles, to shut out any possible addition to the agony already present.
The lines of determination, similarly, about the mouth, are those of the individual who has the courage to say "No" to the tempting morsel when he doesn't need it; and the lines of weakness and irresolution are those of the nature which cannot resist either gastronomic or other temptation. Similarly, the well-known lines of disgust or of discontent about the corners of the mouth are the unconscious contractions accompanying nausea, and preparations to expel the offending morsel whether from stomach or mouth.
If, on the other hand, our first glance shows us that the deepest pain-lines are those about the nostrils and upper lip, especially if the wings of the nostrils can be seen to dilate with each breath, and breathing be faster than normal, our clew points in the direction of some disease of the great organs above the diaphragm—that is, the lungs or heart.