ABSTRACT
Experiments were made to study the reversibility of the effects of hyper-vitaminosis A on embryonic long-bones in vitro.
Limb-bone rudiments from 6-to 7-day chick embryos were cultivated by the watch-glass method, first in medium to which excess vitamin A had been added and then in normal medium. Suitable controls were also grown.
The excess vitamin arrested the growth of the explants and caused the cartilage matrix to shrink and lose its basophilia and metachromasia. The extent of the damage depended upon the length of time spent in + A medium, the concentration of the vitamin, the stage of development of the rudiment when explanted, and the particular rudiment treated.
The degree of recovery was related to the severity of the changes produced by the vitamin. In the shaft these changes were arrested but there was no restora-tion of lost matrix; the cells appeared healthy but resembled osteoblasts rather than normal hypertrophic chondroblasts. The epiphyses also partially recovered and began to enlarge again when transferred to normal medium; they had a high mitotic rate in comparison with the normal controls.