The Energy-Sources in Ontogenesis

Abstract

ABSTRACTThe total carbohydrate in the embryo and in the remainder of the hen’s egg has been quantitatively estimated throughout development. The total carbohydrate in the embryo rises in a regular manner. The total carbohydrate in the remainder of the egg falls from the beginning of development till the seventh day, after which it rises to a peak on the eleventh day before dropping steadily until the time of hatching. The total carbohydrate in the whole egg remains practically constant after the middle of incubation, for then the embryo gains all that the remainder loses. The free glucose in the remainder of the egg falls continuously from the beginning of development till the tenth day, but thenceforward it falls only extremely slowly, if at all. The free glucose in the whole egg suffers a like diminution until the tènth day, after which it rises owing to the accumulation of free sugar in the embryo. There is a current of free glucose yolkwards during the first week of development, flowing in the same direction as the water. The glycogen increases regularly from the beginning of development in the whole egg, but only to any marked extent in the embryo from the eleventh day onward. The extra-embryonic glycogen has a peak about the thirteenth day. The glycogenic function of the embryonic liver is not assumed till the latter part of development; before then it is carried on by the cells of the blastoderm. This closely resembles the mechanism seen in mammalia where the glycogenic function is retained by the placenta till an advanced stage of embryonic life. The peak in the curve for total carbohydrate in the remainder of the egg is partly to be accounted for by the phenomenon of the “foie transitoire.” The ovomucoid glucose (i.e. the total carbohydrate minus the free glucose and the glycogen) falls steadily in the first half of development to reach a minimum about the fifth day, thereafter it rises till the eleventh day only to fall and vanish entirely by the end of incubation. The curve for total cyclose in the developing egg takes a course exactly opposite to that of the total carbohydrate. The gain in total carbohydrate between the seventh and eleventh days coincides remarkably with a loss of fat during the same period, for there is just then a quantity of fat not found in the chemical analyses and not accounted for by the respiration of the embryo, even supposing that all the substance combusted is fat. These amounts are of about the same order and the possibility of a transference of fat to carbohydrate is considered, for the extra carbohydrate certainly cannot be derived from protein. The intensity of absorption of carbohydrate has been calculated in the same manner as that previously used for fat and protein. It is based on analyses of 1320 egg fractions. The curve has a peak at some point prior to the fourth day and descends to a low level by the ninth day, after which it slowly rises. These results afford support for the view already advanced that there are rhythmic permeability-changes in the blastodermal cells. There is a relation of simultaneity between the absorption and combustion of carbohydrate. In this it differs from protein and from fat.