Sympathetic and vagus nerves can to a certain extent control the beating of a bloodless heart. The heart-tissue has acquired the habit of beating, and the habit of listening to advice conveyed to it through these nerves. The self-adjustment of the blood-tubes to the pressure to which they are exposed is exhibited in the adaptation of their degree of contraction to the position of the body—to the weight, that is to say, of the column of fluid which they have to support. Everyone has played the game of “right hand or left.” When the hand is held above the head the blood leaves it, and the hand becomes cold; but if there be need for adjustment, and time is given for the mechanism to come into play, it works to perfection. When we are standing erect, there is neither too much blood in the feet nor too little in the head. But after a fortnight in bed a convalescent finds, the first time that he stands upright, that his legs are quickly engorged—his slippers after a few minutes feel too tight for him—whereas the brain becomes so anæmic that he turns giddy, or even faints. Numberless illustrations of vaso-motor action are met with in daily experience. It is a curious fact that the nerves which control the calibre of the bloodvessels tend to overact their part. When an organ demands more blood, it is supplied at the expense of the rest of the body, and especially of the parts most nearly adjacent. This is partly a mechanical effect. If all the houses in a terrace are supplied with water from a common main, the bursting of a water-pipe in one of them will reduce the supply of its neighbours more than it will reduce the supply of houses in distant parts of the town. But vaso-motor nerves, in their compensating adjustment, go farther than this. A thimbleful of blood removed by a leech produces an effect upon an underlying engorged organ altogether out of proportion to the hydrostatic requirements of the case. “Cupping” the loins diminishes the congestion of the kidneys. This is the explanation of the curative efficacy of various agents which, with improvements in surgery and the introduction of more reliable drugs, have almost disappeared from the surgeon’s armamentarium—scarification, blisters, setons, and the like. Such methods have been relegated to veterinary practice.