[12] Brehm: _Thierleben_, p. 106. Leipzig, 1883. CHAPTER IV _THE CIRCULATION OF THE BLOOD IN THE BRAIN DURING EMOTION_ I When we have drawn on a pair of very tight gloves, we feel, if we pay attention, a slight throbbing in the fingers, corresponding to the rhythm of the cardiac pulsations. This throbbing arises because, by every contraction of the heart, one hundred and eighty cubic centimetres of blood--that is, about as much as can be contained in an ordinary drinking-glass--are driven out of the cavity of the thorax. As this wave of blood penetrates the various organs of the body they swell, as is the case with the arteries which dilate at every pulsation and then resume their former volume. When the hands are unconfined we notice nothing, but if we squeeze them into gloves, or our feet into tight shoes, we feel something beating in fingers and toes. This is the blood gushing in, and as the skin cannot yield as in ordinary conditions, the extremely delicate nerve-filaments which branch into it are pressed at every pulsation. If our finger swells from a whitlow, an inflammation, a knock or a burn, immediately the physiological pulsations, unnoticed before, become continuous, causing an acute, stinging pain. The blood flows more abundantly to the inflamed part, the elasticity of the tissues diminishes, the skin becomes more unyielding, an increased pressure on the nerves ensues, and these, rendered more sensitive through the injury, communicate a painful sensation to the brain which pricks unceasingly, keeping time with the rhythm of the heart. In no organ is the supply of blood so abundant as in the brain; it is sufficient to state that one-fifth of the blood in our body goes to the head. Often, when lying on our side with our cheek on the pillow, we hear the waves of blood passing from the heart to the brain. The arteries, in pulsating, raise the skin, and this movement occasions a slight friction against the pillow, which then propagates itself to the ear. But it is not the beating of the blood against the walls of the vessels, as we feel it on the carotid artery of the neck, or on the radial artery of the hand and elsewhere, which most interests us. A whole world of important facts in the physiology of the emotions and in the circulation of the blood would still be unknown if physicians were still only feeling the pulse, as has been done from the earliest days of medicine until now. With the old methods we should never have succeeded in observing the spectacle of continuous and ever-varying changes which the movement of the blood operates in the brain, the hand, or the foot.