Videos of highlighting the practice of buying, selling of fetal tissue for research use has drawn huge attention. The videos released last week by an anti-abortion group showed how fetal tissue acquired from abortion clinics is used.

The videos accuse Planned Parenthood of selling fetal tissue for profit, but Planned Parenthood has denied the allegations. House Republicans said they will investigate unto the matter and will soon come to a conclusion.

This could be another battle in the nation’s long war over abortion. But now the dispute has raised the questions about who are the buyers and sellers, and what fetal tissue is used for and what the law allows.

Anti-abortion activists and abortion rights supporters demonstrated at the March for Life in Washington in January. Scientists at major universities and government labs have secretly been using fetal tissue for decades. In their view, it is an invaluable tool for certain types of research, including the study of eye diseases, diabetes and muscular dystrophy.

Some of the universities have agreed to talk about the matter only if their names and their universities’ names are withheld, because they have received threats of violence from abortion opponents.

Companies that obtain the tissue from clinics and sell it to laboratories exist in a gray zone, legally. It has been said that the National Institutes of Health spent $76 million on research using fetal tissue in 2014 with grants to more than 50 universities. Furthermore it expects to spend the same amount in 2015 and 2016.

According to researchers, fetal tissue is a uniquely rich source of the stem cells that give rise to tissues and organs, and studying how they develop can provide clues about how to grow replacements for parts of the body that have failed.