But not only is sexuality, and the conduct of the secondary sex characters, connected with the adventures of the adrenal cortex. The development of the master tissues of the body, the brain, the pride and darling of evolution, is in some subtle way correlated with it. The adrenal cortex contains more of the phosphorus-containing substances of the general nature of those found in the central nervous system than any other gland or non-nervous tissues in the body. During human intrauterine life the adrenal glands are large and conspicuous, in the first half of the second month being twice as large as the kidneys. Most of this relatively huge size, which happens in the human alone, and not in other animals, is due to enlargement of the cortex. Should this preponderance of the cortex over the medullary portion not occur in the human, that is, if the proportions remain like those of other animals, the brain fails to develop properly, or an entirely brainless monster is generated. The human brain, therefore, probably owes its superiority over the animal brain, to the adrenal cortex, in development anyhow. The growth of the brain cells, their number and complexity is thus controlled by the adrenal cortex. Besides its action upon the sex cells and the brain cells, the internal secretion of the adrenal cortex acts upon the pigment cells of the skin, blunting their sensitiveness to light. In degeneration of the interior of the gland, which destroys the medulla, but not the cortex, the color of the skin is left unmodified. If, however, the cortex is invaded, as happens most often in the classical tuberculosis of the adrenals which drew the attention of the Englishman Addison to them, then a darkening of the skin, which may go on to a negroid bronzing, follows. That means an increased sensitiveness of the pigment cells of the skin to light. Skin color control may therefore be looked upon as an adrenal cortex function. So much is known about the adrenal cortex. Upon the medulla, the interior gland of the gland, there has been lavished an amount of attention beside which the cortex is to be classed as a neglected wall-flower. Nearly everything that possibly could be determined about an internal secretion has in its case been settled or plausibly guessed at. The cells manufacturing the secretion, its exact chemistry and function, its action upon the blood, the liver and spleen, the heart and lungs, the brain and nervous system, have been minutely investigated, studied and charted. Its source in the food, its fate in the body, its place in the history of the individual and the species, its importance as a weapon in the struggle for existence, and the survival of the fittest have been made the subject of an astonishing number of researches, considering the short period of scarce three decades that intensive science has centered its barrage upon it.