Prof. Halleck says: "All the emotions have well-defined muscular expression. Darwin has written an excellent work entitled, _The Expression of the Emotions in Man and Animals_, to which students must refer for a detailed account of such expression. A very few examples must suffice here. In all the exhilarating emotions, the eyebrows, the eyelids, the nostrils, and the angles of the mouth are raised. In the depressing passions it is the reverse. This general statement conveys so much truth, that a careful observer can read a large part of the history of a human being written in the face. For this reason many phrenologists have wisely turned physiognomists. Grief is expressed by raising the inner ends of the eyebrows, drawing down the corners of the mouth, and transversely wrinkling the middle part of the forehead. In Terra del Fuego, a party of natives conveyed to Darwin the idea that a certain man was low-spirited, by pulling down their cheeks in order to make their faces long. Joy is expressed by drawing backward and upward the corners of the mouth. The upper lip rises and draws the cheeks upward, forming wrinkles under the eyes. The elevation of the upper lip and the nostrils expresses contempt. A skillful observer can frequently tell if one person admires another. In this case the eyebrows are raised, disclosing a brightening eye and a relaxed expression; sometimes a gentle smile plays about the mouth. Blushing is merely the physical expression of certain emotions. We notice the expression of emotion more in the countenance, because the effects are there more plainly visible; but the muscles of the entire body, the vital organs, and the viscera, are also vehicles of expression." These things need but a mention in order to be recognized and admitted. This is the _action_ of the Inner upon the Outer. There is, however, a _reaction_ of the Outer upon the Inner, which while equally true is not so generally recognized nor admitted, and we think it well to briefly call your attention to the same, for the reason that this correspondence between the Inner and the Outer--this _reaction_ as well as the _action_--must be appreciated in order that the entire meaning and content of the subject of Human Nature may be fully grasped. That the _reaction_ of the Outer Form upon the Inner State may be understood, we ask you to consider the following opinions of well-known and accepted authorities of the New Psychology, regarding the established fact that a _physical expression related to a mental state, will, if voluntarily induced, tend to in turn induce the mental state appropriate to it_. We have used these quotations in other books of this series, but will insert them here in this place because they have a direct bearing upon the particular subject before us, and because they furnish direct and unquestioned authority for the statements just made by us. We ask you to consider them carefully, for they express a most important truth.