A week ago, we rode by bus nearly the full length of the old land of Galicia, from L’viv in Ukraine to Kraków, Poland.  Our one long stop was at Belzec, where a moving memorial, the creation of historians and artists, speaks to a double disaster:  the murder of nearly half a million people, predominantly Jews, who were gassed there in 1942 and ’43; and the so-called purification of the region by virtually erasing part (the Jewish part) of a historically complex culture.

The visit spoke to a modern concern, too:  the connections between purity and public health.

The commandant at Belzec, Christian Wirth, had been one of the directors of the Nazi euthansia program, nicknamed T4.  Between 1939 and 1941, T4 killed over 70,000 Germans — mostly full-blooded “Aryans” — who had psychiatric or developmental problems, or congenital conditions, and who were therefore lebensunwerten, unworthy of life.

The T4 program, in its turn, grew out of the Nazi doctrine of racial hygiene — an effort to improve the public’s health by control of breeding.  Racial hygiene was based on eugenics, and led to public health endeavors such as screening for congenital conditions, mandatory sterilization of sexual transgressors and disease carriers, and selective breeding.  The Nazi public health program was much applauded by American public health experts, at least in its first few years.

Once the decision was made to eliminate Jews from Nazi-occupied regions, the experience that Wirth and colleagues acquired through killing the lebensunwerten in T4 was invaluable.  Going from exterminating tens of thousands of mentally ill or developmentally disabled people to eradicating a few million Jews, Gypsies, and other polluters of Aryan health was just a matter of making the process more efficient.

It’s striking how thin the line is between laudable public health goals, like limiting congenital disease through screening, and implementing the concept of race purity.