_Debility_ is almost always accompanied by a disposition to inordinate sleep. The brain is one of the first organs to feel the effects of a diminished amount of blood or a depraved quality of this fluid being supplied, and hence, in old age, or under the influence of a deficient quantity of food, or through the action of some exhausting disease, there is generally more sleep than when the physical health is not deteriorated. The action of certain medicines, and of other measures capable of causing sleep, not coming within the range of ordinary application, will be more appropriately considered hereafter. CHAPTER III. THE PHYSICAL PHENOMENA OF SLEEP. The approach of sleep is characterized by a languor which is agreeable when it can be yielded to, but which, when circumstances prevent this, is far from being pleasant. Many persons are rendered irritable as soon as they become sleepy, and children are especially liable to manifest ill temper under the uncomfortable feelings they experience when unable to indulge the inclination to sleep. It is somewhat difficult to analyze the various phenomena which go to make up the condition called sleepiness. The most prominent feelings are an impression of weight in the upper eyelids, and of a general relaxation of the muscles of the body, but there is besides an internal sensation of supineness, enervation, and torpor, to describe which is by no means easy. This sluggishness is closely allied in character if not altogether identical with that experienced before an attack of fainting, and is doubtless due to a like cause--a deficient quantity of blood in the brain. Along with this languor there is a general obtuseness of all the senses, which increases the separation of the mind from the external world, already initiated by the physical condition of the brain. The liveliest scenes cease to engage the attention, and the most exciting conversation no longer interests. For a time, indeed, such circumstances may dissipate the inclination for sleep, but eventually nature obtains the ascendency and consciousness is lost. Before this event there is usually yawning--a phenomenon strongly indicative of a wearied attention; the head nods and droops upon the breast, and the body assumes that position which is most conducive to ease, comfort, and entire muscular inactivity.