. Chemical embryology. Embryology. 9i6 GENERAL METABOLISM [PT. Ill not show such a fall in the case of the mammalian embryo. Possibly this is due to the fact that we have no analyses of mammalian embryos in the earlier stages, and the earlier, sharper part of the inorganic curve may thus have been missed. Inspection of Col. 13 of Table 108 shows that this decline in ash-content percentage dry weight is in fact more rapid at the beginning than at the end of development. Some fragmentary data for the Jersey cow embryo contained in the paper of Moulton, Trowbridge & Haigh, do not seem to show
. Chemical embryology. Embryology. 9i6 GENERAL METABOLISM [PT. Ill not show such a fall in the case of the mammalian embryo. Possibly this is due to the fact that we have no analyses of mammalian embryos in the earlier stages, and the earlier, sharper part of the inorganic curve may thus have been missed. Inspection of Col. 13 of Table 108 shows that this decline in ash-content percentage dry weight is in fact more rapid at the beginning than at the end of development. Some fragmentary data for the Jersey cow embryo contained in the paper of Moulton, Trowbridge & Haigh, do not seem to show any change between the 185th day of gestation and birth: Percentage Days of gestation Fat Protein Ash 185 232 Birth 14-6 14-0 69-0 69-0 69-0 Il-O 17-4 17-4 ib'O 'arying balance of the chemical Popov has also made analyses of cow embryos, but I have not been able to gain access to his data. Another way of looking at the constituents of the developing em- bryo is to enquire whether the ratios between any two of them change with age. This method was first used by Murray. "Before undertaking my experiments", he said, "I was impressed by what seemed to be a natural scale or gradient, as judged by various criteria, of the chief groups of substances under consideration, namely, salt, carbohydrate, pro- tein, and fat. A tentative predic- tion was considered, that the following ratios would be found to decrease with age during ontogeny water/solid, inorganic/organic, carbohydrate/protein and pro- ; The analyses which Murray and Needham subsequently made confirmed this prediction in every particular. Murray himself attempted to get the carbohydrate/protein ratio by estimating the amount of glycogen in the chick embryo at different stages, but 400 300. ..j^Carbo hydra be Protein + Probe! n • Fat Days-*5 10 Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and ap
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