Cyclic Changes in Blood Calcium, Phosphorus and Fat in Relation to Egg Laying and Estrogen Production

THE DATA brought together here seem useful wholly apart from their contribution to a symposium on the relation of endocrines to skeletal development. In egg-laying vertebrates periods of egg production are associated with surprisingly large changes in serum calcium, lipoid phosphorus and fat; and the ebb and flow of these substances is here regulated by estrogen. In mammals such cyclic changes and such responses to estrogen are so attenuated, so obscure, or so limited in duration that the literature of the subject to date is over-filled with contradiction. Estrogens have a like action on the bones of birds and mammals but it is evident that the blood changes in egg-laying species should be told as a unified, uncomplicated story. In connection with such a statement we draw attention to certain unsolved problems and also present a series of five figures containing hitherto unpublished data.