PHYSIOLOGICAL ONTOGENY

Abstract

Investigations of the chicken embryo during its incubation period show that: 1. The pH and the chloride concentration of the tissues decrease with age; the fall is most rapid between the 10th and the 13th days of incubation. 2. The concentration of total CO2 increases with age. This fact is not considered inconsistent with a possible decrease in the concentration of active bicarbonate ions, since the increased CO2 might well be the result of absorption of calcium carbonate from the shell and its precipitation as bone in the embryo. 3. The concentration of protein increases with age, especially between the 12th and the 16th days of incubation. The fact that the electrolytes change with the greatest rapidity at about 11½ days, the protein at 14 days, and the fat at 16½ days might be taken as a demonstration of the phenomenon of unequal development in the realm of biochemical differentiation and consequently that some notion of order, depending upon molecular reactivity and mobility would describe the process better than any concept of dynamic equilibrium.