Dr. Dickson[9] regards an increased determination of blood to the cerebral mass, and its consequent congestion in the larger vessels of the brain, as necessary to the induction of sleep. In his very excellent work on Epilepsy, Dr. Sieveking[10] says: “Whether or not there is actually an increase in the amount of blood in the brain during sleep, and whether, as has been suggested, the choroid plexuses become turgid or not, we are unable to affirm otherwise than hypothetically; the evidence is more in favor of cerebral congestion than of the opposite condition inducing sleep--evidence supplied by physiology and pathology.” Dr. Sieveking does not, however, state what this evidence is. Barthez[11] is of the opinion that during sleep there is a general plethora of the smaller blood-vessels of the whole body. He does not appear to have any definite views relative to the condition of the cerebral circulation. Cabanis[12] declares that as soon as the necessity for sleep is experienced, there is an increased flow of blood to the brain. To come to more popular books than those from which we have quoted, we find Mr. Lewes,[13] when speaking of the causes of sleep, asserting that: “It is caused by fatigue, because one of the natural consequences of continued action is a slight congestion; and it is the _congestion_ which produces sleep. Of this there are many proofs.” Mr. Lewes omits to specify these proofs. Macnish[14] holds the view that sleep is due to a determination of blood to the head. That a similar opinion has prevailed from very ancient times, it would be easy to show. I do not, however, propose to bring forward any further citations on this point, except the following, from a curious old black-letter book now before me, in which the views expressed, though obscure, are perhaps as intelligible as many met with in books of our own day: “And the holy scripture in sundrie places doth call death by the name of sleepe, which is meant in respect of the resurrection; for, as after sleepe we hope to wake, so after death we hope to rise againe. But that definition which Paulus Ægineta maketh of sleepe, in my judgment, is most perfect where he saith: Sleepe is the rest of the pores animall, proceeding of some profitable humour moistening the braine. For here is shewed by what means sleepe is caused; that is, by vapours and fumes rising from the stomache to the head, where through coldness of the braine they being congealed, doe stop the conduites and waies of the senses, and so procure sleepe, which thing may plainly be perceived hereby; for that immediately after meate we are most prone to sleepe, because then the vapours ascende most abundantly to the braine, and such things as be most vaporous do most dispose to sleepe, as wine, milke, and such like.”[15]