306. The vital power which it has been shown (298) is possessed by the arterial trunks and branches, is still more intense in the minute capillaries. If alcohol, strong acetic acid, naphtha, and other stimulating fluids, be injected into the arteries of a living animal, it is found that they are not transmitted through the capillaries at all, or, at all events, that they make their way through them with extreme difficulty; whereas mild, unirritating fluids pass with rapidity and ease. Wedemeyer exposed and divided the main artery in the fore-leg of a horse, together with the corresponding vein in the shoulder. Several syringes-full of tepid water were now injected into the lower end of the artery. The gentlest pressure was sufficient to force the fluid through the capillaries. At each injection the water issued in a full stream from the aperture of the vein, the flow of the fluid ceasing as soon as the injection was stopped. Next, instead of water, four syringes-full of pure cold brandy were injected. To propel this fluid through the capillaries, so as to render its smell and taste perceptible at the aperture of the vein, required a great degree of pressure; and when at last the fluid issued from the vein, it merely trickled in a feeble stream. The experiment being repeated on another horse with vinegar, six syringes-full of which being injected in rapid succession, at first this fluid passed as easily as water, afterwards it flowed with greater difficulty and in a small stream; before long the force required to propel it was extreme, and at last the obstruction to its passage became complete, so that no fluid whatever issued from the vein. These experiments, whenever repeated, afforded the same result, and they demonstrate that the capillaries are capable of being stimulated to contract upon their contents, and that they can contract with such force as to stop the current. It is manifest that the power by which they do this is vital, because after death all fluids, the mildest and the most acrid, pass through them with equal facility.