The Presidential Commission for the Study of Bioethical Issues on Thursday issued the second half of a pair of studies requested by President Obama following last year’s revelation that U.S. government scientists in the 1940s intentionally infected hundreds of people in Guatemala with gonorrhea and syphilis as part of a public-health research project. In the first study, issued in September, the ethics commission blamed the Guatemala experiments on a series of top university and government officials. In its latest report, the commission focuses on ways of ensuring that such abuses are not repeated. It says that current procedures afford “substantial” protections for human test subjects, but recommends a number of changes. It also presses for the consideration of a new federal guarantee of care or compensation for research subjects if anything goes wrong.