41.   One logical source of embryonic cells would be the surplus embryos created through in vitro fertilization that infertile couples no longer planned to use.

42.   One of those directions is research on transplanting human embryonic cells, or stem cells.

43.   One, the least preferred, would be to set up a bank with enough different human embryonic cells that most patients could be matched.

44.   One is that biologists have not yet identified the natural signals that are assumed to govern the differentiation of embryonic cells in the body.

45.   Private companies and university researchers supported with nongovernment money have been free to derive embryonic cell lines from human embryos.

46.   Researchers have routinely generated new strains of mice by manipulating mouse embryonic cells, and some aspects of this technology may prove useful for improving human embryonic cells.

47.   Scientists are releasing reports on Friday of two major advances in the concept of using embryonic cells to regenerate human tissues.

48.   Second, replacement tissues could be generated from human embryonic cells by driving them down the appropriate lineages with cytokines and other agents.

49.   Some conservative lawmakers have vowed to prevent public funding because the embryonic cells can only be obtained from human embryos or aborted fetuses.

50.   Since mouse embryonic cells already can, he said, it is theoretically possible.