As discussed elsewhere, one reason is that at the time Syphilis response was significantly different in Africans. Trials like this had been previously run on Eu

As discussed elsewhere, one reason is that at the time Syphilis response was significantly different in Africans. Trials like this had been previously run on Europeans, and 731 would presumably include east Asians and ran for a handful of years, not decades. Unlike Unit 731, they didn't infect anyone and it was an observational study.