THE CHEMISTRY OF EMBRYONIC GROWTH

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Abstract
1552 pig embryos, 4-240 mm. in length, were analysed. After dehydration in acetone and extraction with absolute ether and alcohol, the nitrogenous compounds were studied by the Van Slyke N distribution method. Water content, total S, total ash, glutathione, and tyrosine were also determined. During development there was a decrease in those N fractions reacting as arginine and histidine and an increase in lysine, although the total bases remained essentially constant at 38-39% of the total N. Humin N, amide N, and cystine remained practically unchanged. Total N showed an early decrease until the 30 mm. stage and then remained remarkably constant. Water rapidly decreased in the early stages from 94.67% at the 6-7 mm. stage to 91.71-91.02% at the 15-160 mm. stages, to 90.34% at the 200 mm. stage, and to 88.7% in the 240 mm. embryos. Glutathione showed a rapid increase to a peak at the 30 mm. stage, a rapid decrease at the 40 mm. stage, followed by a slower but continuous fall throughout the later growth stages. Total S showed an increase to the 50 mm. stage and then a gradual decrease. Ash increased in the very early stages, followed by a slight decline, and then a continued increase as the skeletal structure developed. Tyrosine showed a gradual decline throughout the entire developmental period. The paper discusses the significance of the changes and their relationship to tumor chemistry and evolutionary processes.

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