The concept of humoral control—the direction of bodily processes by complex organic fluids—has gained ascendancy in recent decades, and enlisted the interest of more than humoral specialists. The present summary of current humoral research accordingly pays particular attention to its bearing on physiological theory, and its contribution to our general knowledge of the integrative forces which maintain the unity of the individual.

The ancient theory of the four hundred, which dominated medicine from the time of Hippocrates to the beginning of the seventeenth century, contained in rudimentary form the notion that chemical agents transported in the blood controlled biological and emotional states. This notion was apparently discredited forever in the eighteenth century when it was supplanted by the galvanic theory that control was exercised through electrically transmitted neural impulses. Near the beginning of the present century, however, experimental evidence in turn discredited the electrical theory, and laid the groundwork for the modern humoral concepts discussed in these pages.

Specifically covered are the development of endocrinology, the discovery of digestive hormones, hormonal regulation of metabolism, the action of trophic hormones, interactions within the endocrine system, chemical transmission of neuronal impulses in the central and peripheral nervous systems, and the control exercised by the central nervous system, particularly the hypothalamus, over endocrine and other secretory processes.