In this connection the work of Robertson (13) should be mentioned. He separated a crude lipoid fraction from the anterior lobe of the pituitary of the ox to which he gave the name tethelin. He carried out extensive experiments on the growth of mice designed to show the effect of tethelin. There was offered no evidence that a definite substance was isolated, for no adequate attempt was made to purify the active principle which it was believed to contain. Furthermore, the substance was, in his experiments, superimposed upon a mixed diet of considerable complexity, which was adequate for the nearly normal nutrition of the mouse. It is not possible to intelligently discuss Robertson's results, therefore, in connection with the dietary problems which form the theme of this book.