Dr. Riddle's pigeons laid golden eggs, all yolk with neither shell nor white, because he removed their thymus glands. Dr. Rowntree's husky baby rats played precociously because he stimulated their thymus glands with sweetbread extract. Then Dr. Riddle turned another neat trick by giving sweetbread extract to his thymectomized pigeons, which promptly began to lay normal, shell eggs.
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