Organ growth in hyperoxic and hypoxic chick embryos

Chick embryos and their organs were weighed in order to compare retarded growth with accelerated growth. Growth was quickened by incubating eggs in 60% O2/40% N2 and slowed by covering part of the shell of eggs incubated in air. A control group was incubated in air without any covering. At two-day intervals from the twelfth to the eighteenth days inclusive, eggs were opened and the embryos dissected and weighed. An organ was 'spared' if it differed from its control weight proportionately less than did the whole embryo. Covered eggs were opened only on the eighteenth day and showed sparing of brain and heart and hepatic stunting in excess of body stunting. Hyperoxic eggs spared brain and liver during the period in question, but the heart grew proportionately more than the other tissues between days 16 and 18. These data show that the availability of oxygen alters the rate of embryonic growth, and induces differential growth among individual organs.