Thyroid deficients, however, are definitely the opposite. They are quite conscious of the limited reserve of energy at their command. Also that they need plenty of refreshing sleep. Early to bed and late to rise remains the leading maxim of health for them. In addition they find it necessary to sleep during the day. Forty winks or more in the afternoon makes a good deal of difference to them. Taciturn, inarticulate, lazy, slow, tired, are the adjectives applied to them by their friends as well as by their enemies. All because of an insufficient or inefficient supply of the thyroid's iodine to their cells. The mobility of energy in an organism is a measure of the amount of active iodine in it. The physiologic synonyms for "energetic and lazy" are "well-iodinized" and "poorly iodinized." Sensitivity, the ability to discriminate between grades of sensation or acuteness of perception is another thyroid quality. Just as the thyroid plus is more energetic, so is he more sensitive. He feels things more, he feels pain more readily, because he arrives more quickly at the stage when the stimulus damages his nerve apparatus. The electric conductivity of his skin is greater, sometimes a hundred times greater, than the average. Conversely the thyroid deficient type has a low discriminative faculty. Galton has recorded that idiots hardly distinguish between heat and cold and that their sense of pain is so obtuse that some of the more idiotic seem hardly to know what it is. Cretins may moan but never shed tears. Energy and sensitivity in an individual should direct attention to the thyroid element predominating in his composition. Lack of energy and insensitivity to the degree of thyroid insufficiency in their make-up. MEMORY, JUDGMENT, AND POISE In between sensitivity and energy, the sensation and the reaction, comes a passage of the stimulus through the gauntlet of the stored past experience of the individual known as memory. Many hypotheses have been advanced by philosophers, psychologists and physiologists to explain the phenomenona of memory. To conceive of memory materially at all one must admit some sort of memory trace as the basis for the persistence of memory. This memory deposit facilitates the occurrence of the chemical reaction constituting the memory along the same path the next time. Forgetting then consists in a disappearance of these memory traces or deposits. Forgetting is greatest in the first hour after remembering, more than half of the memory trace being lost in that time. Comparison of the curve of forgetting, and the curve of diffusion of a colloid like gelatine from its solution, into a surrounding medium, shows them to be exceedingly similar. Forgetting may be explained by some such loss of the memory trace or deposit into the blood continually flowing by it.