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. To this mechanical pressure on the Cerebellum, the illustrious Van Sweiten seems to attribute the motion of the Heart: “Cerebelli enim actio in Cor per Nervos, pendet ab ipsa actione Cordis per Arterias[8].” Tho’ the contraction of the Heart is evidently the efficient cause of the Blood’s motion, and consequently of the secretion of these spirits in the Cerebellum, yet, without these spirits, the action of the Heart could not be performed. These two causes appear to act in a circle, and mutually depend on each other. Hence Hippocrates divin’d, ὁλον το ζωμα κυκλος εστι. These also convey the idea of a perpetuum mobile; since, as long as life lasts, an animal is really such, and far excels any machine that human art has been yet able to make, or (in the opinion of many philosophers) will ever invent. The laborious Hoffman ascribes a great deal to this pressure on the Brain, where he says, “[9]Declivior cubitus sanguinis regressum quodammodo impedit, quia per venas jugulares descendere debet, quod elatiori capite commodius peragitur. Hinc, capite nimis demisso ac depresso, profundiores somnii cum insomniis, fiunt, universo corpore torpor inducitur. Eadem ratione, si quis facie prona velut in mensa, in somnum delabitur. Ob difficiliorem sanguinis regressum, gravitatem capiti, et ingenio stupiditatem accersit.” “[10]Sed etiam mechanicæ causæ somnum producunt, compressio nempe Duræ Matris, aut Cerebri, quæcunque nata a Sanguine effuso, inpacto Osse, aquæ in Ventriculis copia.”