Clinicians have long been familiar with diseases of the endocrine system in which alterations of bone shape occur, and chemical investigations have now shed some light on these conditions. Of all hormones the growth-promoting factor of the anterior pituitary gland is undoubtedly the most potent in inducing skeletal change. The pituitary may exert a direct control over bone growth and the effects of other hormones—e.g. those of the thyroid and parathyroid glands and the gonads—may have to be explained on the basis of their effects on the production of this growth-promoting factor. On the other hand, the converse may hold, viz. the action of the pituitary may be indirect. While there is considerable quantitative information about the gross metabolic changes in bone disease, there is little or no information about the nature of the physicochemical alterations, if any, produced [Logan, 1940]. It is well known that there is an increase