The growth, development and phosphatase activity of embryonic avian femora and limb-buds cultivated in vitro

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Abstract
The isolated femora of 51/2-day and 6-day fowl embryos were found to have a remarkable capacity for self-differentiation. During cultivation in a watch-glass the 5 1/2-day femora increased to more than 3 times their original length. Their gross anatomy remained comparatively normal and they underwent a remarkably normal histological differentiation. During cultivation the isolated femora synthesized a phosphatase; no phosphatase was present in the tissue at the time of ex-plantation and the gross amount formed increased with the age of the culture. The ratio offphosphatase to the dry weight of the femur increased during cultivation from zero to a maximum and then declined. The in-crease corresponded with the progress of histological differentiation and the decline with degeneration. The maximum value of this ratio was higher than that found for normal embryonic femora. Undifferentiated 3-day embryonic limb-buds cultivated in vitro gave rise to small-celled cartilage only. Such explants after culti-vation were completely devoid of phosphatase, thus confirming the view that the enzyme is formed by cartilage only if hypertrophic cells are present.