THE FREE CARBOHYDRATE OF THE DEVELOPING CHICK

1. The free carbohydrate in the chick embryo has been estimated quantitatively throughout its development. In absolute amounts it rises with the gromth of the embryo, but as per cent. of the weight it falls in the later part of incubation. 2. Expressed as per cent. of the total carbohydrate, the free carbohydrate curve presents a well-marked peak at the eleventh day. 3. The glycogen/glucose ratio rapidly changes at the same time, rising from well below unity to well above unitv. 4. It is shown that this critical point in development coincides with the appearance of the islets of Langerhans in the embryonic pancreas and the initiation of the glycogenic function in the liver. From this it is concluded that insulin is not formed by the growing embryo till the eleventh day of incubation or a little before, and this is discussed with reference to other hormones and the loss of totipotential plasticity by the grow-ing embryo. 5. In the early stages of development in the chick there is a larger proportion of glucose not accountecd for by glycogen or by free glucose than at any other time. This unidentified combined glucose is probably mucoprotein carbohydrate, and its importance in the early stages may be correlated with the primitive gelatinous intercellular matrix in which the embryonic cells at that time grow and migrate. 1 The thanks of the writer are due to Professor Sir F. G. Hopkins, F. R. S., and to the Government Grant Committee of the Royal Society. Very similar evidence has been adduced for the hormones of the following glan Pituitary ( Hogben and Crew ), testis ( Kudo ), and thymus ( Trinka ).