Wöhler in 1828, by synthesizing urea, performed what up to that time was considered to be impossible, namely, the artificial production of an organic substance from mineral matter. Since then up to the present time there have been few advances in biology which seem so startling as do those which have been made in recent years, resulting in the establishment of a technic whereby animal tissues may be made net only to live, but also actually to grow outside of the body.
Harrison,1 working at Johns Hopkins, in 1907, was the first actually to cultivate tissues outside the body. He found that the embryonic tissue of frogs, when transplanted into coagulable lymph, would develop normally. Burrows2 in 1910, working under Harrison at Yale, was the first to grow normal tissues of warm-blooded animals; he used chick embryos in his experiments. Finally Carrel and Burrows3 at the Rockefeller