In 1972, Pediatric Research journal published a paper submitted by researchers from the Department of Pediatric Research at New York State and Mount Sinai School of Medicine of the City University of New York in collaboration with a researcher from the Departments of Medical Chemistry and Obstetrics and Gynecology of the University of Helsinki in Finland. The paper was titled, “Development of Mammalian Sulfur Metabolism: Absence of Cystathionase in Human Fetal Tissues.” The fact that they used fetuses is stated right in the title. The researchers “examined the development of the transsulfuration pathway in 58 human fetuses obtained at therapeutic abortion during approximately the 2nd-6th month of gestation” as well as in premature and full term infants who died shortly after birth. They were trying to determine whether cysteine is an essential amino acid in “immature humans,” so they needed to analyze kidneys and brains at different developmental stages.Share
The fetuses presented a special test case. Since the fetuses were still alive at the beginning of the experiment in their mothers’ wombs, “in vivo” experiments were possible. This phrase “in vivo” is Latin and means “within the living.” With already deceased specimens, they could only measure the presence of amino acids after death. This type of analysis is an “in vitro” (in the glass, think in vitro fertilization) procedure. With the still-living fetuses, they could actually inject a known amount of amino acids, S-L-methionine and S-L-cysteine, “in vivo” into a living fetus and test how much of these substances were incorporated into fetal organs via the biological machinery of life over a set amount of time. The researchers therefore conducted the “in vivo” experiments by surgically cutting open the uterus of the mother, lifting out the living fetus with the umbilical cord still attached, and injecting the amino acids into the umbilical vein.
Then they waited 10 minutes with the heart still beating and the fetus still moving to allow the body to distribute and metabolize the amino acids. After 10 minutes, they cut the umbilical cord, dissected the brain and liver from the body of the fetus, and dropped the organs into liquid nitrogen to await analysis. (Read more.)