61.   But now, as scientists are eyeing human embryo cells as material for research, the experiment is giving rise to a thorny philosophical question.

62.   But it has also produced tens of thousands of human embryos, microscopic clusters of cells, frozen in tanks in laboratories around the nation.

63.   But opponents of abortion, including many members of Congress, object to the federal financing of any research that requires the destruction of a human embryo.

64.   But Racowsky added that she was troubled by the notion that the method did not really create human embryos.

65.   But some legal experts have no doubt that it should be regarded from the start as a human embryo.

66.   But some stem cell research could involve the cloning of human embryos merely as experiments, an offshoot that is far more controversial.

67.   But the lines become blurred over the type of research being conducted by ACT and other bioresearch firms seeking to create human embryos strictly for their stem cells.

68.   But scientists cannot use federal money to extract the stem cells from human embryos.

69.   But the most versatile stem cells are those from four-day-old human embryos, which consist of a tiny sphere of cells.

70.   But some stem cell research could involve the cloning of human embryos for experiments, an offshoot that is far more controversial.