An “experimental serum” arrived in Liberia and was administered to one of two infected U.S. charity workers, the group Samaritan’s Purse said Thursday. There was only enough for one of the two infected workers however, so Dr. Kent Brantly asked that the serum be used on his colleague, who is in stable but serious condition, while he receives an alternative treatment using blood transfused from a survivor of the virus. “Yesterday, an experimental serum arrived in the country, but there was only enough for one person. Dr. Brantly asked that it be given to Nancy Writebol,” Franklin Graham, president of Samaritan’s Purse, said in a statement. “However, Dr. Brantly received a unit of blood from a 14-year-old boy who had survived Ebola because of Dr. Brantly’s care. The young boy and his family wanted to be able to help the doctor that saved his life.” The specific serum that Writebol will receive was not disclosed.