A fairly high blood pressure is necessary for bodily well-being, because only thereby is the brain assured of sufficient nourishment. To see why this is so, we have only to remember that the brain is unfavorably situated for receiving ample supplies of blood. It is at the top of the body, so that the influence of gravity has to be overcome in forcing blood up to it. Also it is completely inclosed in the bony skull, which it in turn fills so completely that there is almost no room for the accommodation of extra blood in it. In all other parts of the body a rise in blood pressure stretches the arteries and so leads to there being actually more blood within them, but there is no room for the arteries in the brain to stretch, so that the total quantity of blood in the brain cannot vary greatly from time to time. The only way in which an increased blood supply can be obtained is by causing the blood to flow more rapidly. This is precisely what happens every time the blood pressure in the body rises. Whenever the vasoconstrictor center sends nervous discharges into the blood vessels of the skin and abdominal organs, causing them to contract, there is a diversion of blood from them directly into the skeletal muscles and also a rise in blood pressure due to the increase in resistance to the circulation, which causes blood to flow more rapidly through the brain. The net result, then, is improvement in the blood supply to the skeletal muscles and to the brain. So important is the blood supply to the brain that the vasoconstrictor center discharges actively throughout the waking part of the day. If for any cause the activity of this center diminishes, there will be an increased circulation in the skin and in the abdominal organs, the blood pressure will fall, the circulation through the brain will decrease, and along with it there will be a decrease in brain function. After this passes a certain point unconsciousness will result. This is what happens when one faints. For some reason or other the vasoconstrictor center becomes inactive, and the series of events just described is set in motion. Fainting ordinarily cures itself automatically, because when consciousness is lost, the individual falls over; this brings his head down on the level with the rest of his body, makes it easier for the blood to flow through it, and so in a moment or two consciousness will be regained. It is a mistake to try to scramble to one’s feet immediately, because until the vasoconstrictor center recovers its ordinary activity, raising of the head above the level of the rest of the body is bound to result in its failure to receive sufficient blood, and so faintness will come on again. It has long been a practice to dash cold water in the face of a fainting person. The physiological value of this is in the sudden stimulation of the sensory nerves in the face by which is set up a stream of nervous discharges which will play upon the vasomotor center, and arouse it again to