It was proved by my balance that, at the slightest emotion, the blood rushes to the head. But this did not satisfy me. I wished to analyse this phenomenon more minutely, and constructed other new instruments in order to study it in all its particulars, and to follow the blood while it streams from hands, feet, and arms to the brain. I have traced the pulse for hours together, not of one part only, but nearly always of several parts of the body at the same time--of the brain, the hands, the feet, noting the slightest changes which the activity of thought, external impressions, noises, or dreams produced on the blood-vessels, waking or sleeping. It was already known that the pulsations of the heart augment under the influence of food and drink, but no one had observed, by means of other instruments, certain modifications which the form of the pulse undergoes, and which are so characteristic that I need now only see the curve of a single pulsation of hand or foot in order to know whether the person had eaten or was fasting. Again, between two pulsations presented to me, I can distinguish that of the thinking and that of the absent-minded man, that of the sleeper and that of one awake, that of one who is warm and that of one who is cold, that of the tired man and that of him who has rested, that of one who is afraid and that of one who is tranquil. One of my literary friends came one day to visit me in the laboratory, in order to convince himself with his own eyes of these results, which seemed to him scarcely credible. I proposed to make an experiment upon himself, to see whether any change would be observable in his pulse when he passed from reading an Italian book to a Greek one. At first he laughed at the idea, but when we put it to the proof, we found that with him also the pulse of the wrist changed considerably when he passed from an easy work to the more difficult one of translating, unprepared, a passage from Homer. The vital processes are the more active the greater the rapidity with which the blood circulates in our body; but in order to accelerate the movement of the blood, the blood-vessels must contract. What we notice in the course of rivers, namely, that the current becomes quicker at that point where the bed is narrower, takes place also in our circulatory system. When we are threatened by a danger, during fear, emotion, when the organism must develop its strength, an automatic contraction of the blood-vessels takes place, which renders the movement of the blood more rapid in the nerve-centres. It is on this account that the vessels at the surface of the body contract, and we grow pale from fright or during violent emotion. I have measured exactly the amount of blood which retreats from hands and feet during the slightest emotions, also the number of seconds between the moment when the emotion arises and that when the pallor is greatest, but this is not the place for statistics.