This opinion is mainly, if not entirely, due to the fact that it is confounded with stupor, from which, both in its causes and effects, as has already been shown, it differs in every essential respect. Somnolence is nothing more than an inordinate tendency to sleep. When manifested in a slight degree it is difficult, without careful examination and a thorough inquiry into the history of the case, to distinguish it from moderate stupor. It is of course very important that the distinction should be made; for, in reality, somnolence is ordinarily no very serious disorder, and is generally symptomatic of eccentric disease, whereas stupor almost invariably results from organic brain affections, from cerebral injuries, or the circulation of poisoned blood through the encephalic blood-vessels. Whatever lessens the amount of blood normally circulating through the cerebral vessels, tends to the production of somnolence. It is hence a condition frequently witnessed in those whose powers of life have been reduced by long-continued disease, by excesses of various kinds, or by affections which essentially consist in enfeeblement of the organism. It is generally met with in the aged, in whom the circulatory organs have lost their pristine vigor. Many cases of very troublesome and persistent somnolence, having an origin such as I have mentioned, have come under my notice: ordinarily they present no difficult features of treatment, the indications being to increase the tone of the system by stimulants, tonics, nutritious food, and moderate exercise in the open air. These measures will invariably succeed if there be no organic difficulty. Somnolence, however, is sometimes due to structural changes which interfere with the free passage of blood through the cerebral vessels. It may hence be caused by emboli, which, obstructing the arteries, prevent the normal amount of blood reaching the brain substance. It may also be caused by tumors, which, pressing on the arteries supplying the brain, act in like manner. In such cases it is of secondary importance. A very curious affection, known as the “Sleepy Disease,” has been described as endemic in certain regions of Africa. The following extract[143] gives a graphic description of the malady: