As the Blood must lose most of the motion which it receives from the Heart, in passing through the infinite vascular ramifications, and fine filtres of the Brain, there scarce appears, even in an erect position of the Body, any propelling power to push it back again to the Heart, except we admit the pulsation of the small Arteries belonging to the coats of the Sinuses, and its own gravity. But in an horizontal position, the Blood has not the advantage of its gravity to accelerate its motion through the Jugular Veins; therefore it must move slower, and must be more subject to obstruction in the vessels of the Brain. Hence we see the use of pillows is to promote and facilitate the return of the Blood through the Jugular Veins: hence we may also observe, the uneasiness and danger attending the too common method of making the feet of beds higher than the heads, since a stoppage of the Blood is always productive of dangerous consequences; of which any one may be soon convinc’d by stooping the Head for a short time; and it will appear, that the Blood is by this means collected in the Veins of the Face, which will produce a Vertigo, and, if long continued, may bring on an Apoplexy. Hence we sometimes hear of people dropping down dead, upon stooping to buckle their shoes. These instances should deter some from putting their pillows under their feet, in order to make the Blood settle in their faces, and to decorate the external part of their Heads at the expence of the internal.
Notwithstanding the inconveniences and bad effects which may arise from the Blood’s delay in the Brain, yet, its being sent to the Head in sleep in a greater quantity, may serve many necessary purposes, and render sleep more beneficial and refreshing to animals. First, by distending the Blood-vessels of the Cerebrum, increasing the pressure on that part, and by that means producing sleep. Secondly, by promoting the secretion, and preparing a store of animal spirits to supply the expence of the ensuing day. Thirdly, by gently encreasing the pressure of the Blood-vessels on the Cerebellum, and perhaps determining a greater quantity of the nervous influence to the Heart, respiratory Muscles, and other parts, whose Nerves spring from that fountain of life. This pressure on the Cerebellum may concur with the rarefaction of the fluids, to render the motions of these organs more regular and vigorous in sleep.