Britain's first human-animal hybrid embryos have been created, forming a crucial first step, scientists believe, towards a supply of stem cells that could be used to investigate debilitating and so far untreatable conditions such as Alzheimer's disease, Parkinson's and motor neurone disease. Lyle Armstrong, who led the work, gained permission in January from the Human Fertilisation and Embryology Authority (HFEA) to create the embryos, known as cytoplasmic hybrids". His team at Newcastle University produced the embryos by inserting human DNA from a skin cell into a hollowed-out cow egg. An electric shock then induced the hybrid embryo to grow. The embryo, 99.9% human and 0.1% other animal, grew for three days, until it had 32 cells. Eventually, scientists hope to grow such embryos for six days, and then extract stem cells from them. The researchers insisted the embryos would never be implanted into a woman and that the only reason they used cow eggs was due to the scarcity of human eggs. Cardinal Keith O'Brien used his Easter sermon to denounce what he called experiments of "Frankenstein proportion" and called the bill a "monstrous attack on human rights, human dignity and human life". Catholics object to the idea of putting human and animal DNA in the same entity and to the notion of creating what they regard as a life for the purposes of research, a life that will then be destroyed.