The order in which the muscles lose their power is in general well marked, and bears a distinct relation, as Cabanis[30] has pointed out, to the importance of their functions. Thus, the muscles which move the arms and legs become relaxed before those which support the head, and the latter before those which maintain the erectness of the back. This, however, is not always the case, for, as we have already seen, individuals will occasionally walk, and keep their position on horseback, while in a sound sleep, and all of us have seen persons slumbering in church, their heads dropping on their breasts, but yet firmly holding their prayer-books in their hands under the pretense of going through the services. As regards the senses, the sight is of course the first to be lost in ordinary cases--the closure of the eyelids interposing a physical obstruction to the entrance of light. Even when the eyelids have been removed, or from disease cannot be closed, the sight, nevertheless, is the first of the special senses to be abolished. Some animals, as the hare for example, do not shut the eyes when asleep; but even in them the ability to see disappears before the action of the other senses is suspended. These latter are not altogether abolished during sleep; their acuteness is simply lessened. Taste is the first to fade, and then the smell; hearing follows, and touch yields last of all, and is most readily re-excited. To awake a sleeping person, impressions made upon the sense of touch are more effectual than attempts to arouse through any of the other senses; the hearing comes next in order, smell next, then taste, and the sight is the last of all in capacity for excitation. During sleep the respiration is slower, deeper, and usually more regular than during wakefulness. The vigor of the process is lessened, and therefore there is a diminution of the pulmonary exhalations. In all probability, also, the ciliated epithelium which lines the air-passages functionates with reduced activity. Owing to this circumstance and to the general muscular torpor which prevails, mucus accumulates in the bronchial tubes and requires to be expectorated on awaking. The circulation of the blood is rendered slower. The heart beats with more regularity, but with diminished force and frequency. As a consequence the blood is not distributed to distant parts of the body so thoroughly and rapidly as during wakefulness, and accordingly the extremities readily lose their heat. Owing to the reduction in the activity of the respiratory and circulatory functions, the temperature of the whole body falls, and coldness of the atmosphere is less easily resisted.