If, in the moments preceding sleep, when the mind is comparatively quiet, we make an effort to fix our thoughts on something, we notice how they vacillate, disappearing and reappearing, as though we were in a boat and our heads were lifted from time to time above the waves. Even when awake we find ourselves only too often in this humble bark in which every puff of wind drives us far from the shore we wish to reach, when impetuous currents of thought prevent our entering the haven, or when the waves open to plunge us into unfathomable depths out of which we can see no horizon. III But in order better to see the link which binds the substance of our organism to the activity of thought, the correlation between the nutrition of the body and the mental state, or, as one is accustomed to say, the relation between body and soul, let us carefully notice what takes place when a number of friends are assembled at table. After a few cheerful remarks made by the most jovial as they take their places, a certain gloom spreads over the company. One might almost think only a few were sociably inclined. Someone attempts to break the ice, but it is a failure; one feels that the conversation is forced, jerky, altogether wanting in sparkle. Little by little the guests brighten up. A hum ensues, then a confused buzz, like the tuning of the instruments of an orchestra, which rapidly increases in pitch, as though each were trying to make his voice heard above his neighbour’s. It seems as though something in their brains had been loosened and the vocal cords had gradually got into working order. At dessert even the more taciturn, if they have done full justice to the banquet, pour forth an unceasing stream of conversation. Moody faces become smiling, and melancholy gives place to gaiety. The cross-fire of talk, the hot discussions, the frequent bursts of laughter, the lively play of feature, the witty interruptions, the excited gesticulations, all show a hundredfold increase of vital action. And from the glowing faces, the sparkling eyes, we know that the blood is rushing in abundance to the brain. The tongue is loosed, ideas accumulate in the mind, as though some kind hand had set the rusty wheels of thought in motion and poured oil on the hinges of the vocal mechanism.