Scientific research into the functioning of the ductless glands and their secretions throws a new light on this problem. Not long ago these glands were a complete enigma, owing to the fact that they are not provided with excretory ducts. It has just recently been shown that these organs, such as the thyroid, the pituitary, the suprarenal, the parathyroid and the reproductive glands, exercise an all-powerful influence upon the course of individual development or deficiency. Gley, to whom we owe much of our knowledge of glandular action, has asserted that "the genesis and exercise of the higher faculties of men are conditioned by the purely chemical action of the product of these secretions. Let psychologists consider these facts." These internal secretions or endocrines pass directly into the blood stream, and exercise a dominating power over health and personality. Deficiency in the thyroid secretion, especially during the years of infancy and early childhood, creates disorders of nutrition and inactivity of the nervous system. The particular form of idiocy known as cretinism is the result of this deficiency, which produces an arrest of the development of the brain cells. The other glands and their secretions likewise exercise the most profound influence upon development, growth and assimilation. Most of these glands are of very small size, none of them larger than a walnut, and some--the parathyroids--almost microscopic. Nevertheless, they are essential to the proper maintenance of life in the body, and no less organically related to mental and psychic development as well. The reproductive glands, it should not be forgotten, belong to this group, and besides their ordinary products, the germ and sperm cells (ova and spermatozoa) form HORMONES which circulate in the blood and effect changes in the cells of distant parts of the body. Through these HORMONES the secondary sexual characters are produced, including the many differences in the form and structure of the body which are the characteristics of the sexes. Only in recent years has science discovered that these secondary sexual characters are brought about by the agency of these internal secretions or hormones, passed from the reproductive glands into the circulating blood. These so-called secondary characters which are the sign of full and healthy development, are dependent, science tells us, upon the state of development of the reproductive organs.