In the hours after the 9/11 attacks, New York City hospitals and blood banks filled with willing donors hoping to be of use on a helpless day. Primum Non Nocere, director James Reynolds’s starchy but persuasive argument doc about the dubious merits of blood transfusions, suggests that impulse is a measure of the blood industry’s success. A working history of the transfusion—beginning with its emergency inception on the battlefields of World War I—gives way to a poorly organized critique of the culture of authority that gathers around “breakthrough” medical practices and the dearth of scientific research into the repercussions of a now-entrenched protocol. An international assortment of nay-saying doctors testify to camera; amid the wonky talk about hematocrits and hemoglobin one sentiment makes itself most plain: “Laypeople think we know exactly what we’re doing.” Reynolds’s point is that they don’t, especially when it comes to infusing one human being with another’s blood. Scattered construction—an unceasing onslaught of information is broken up by random B-roll footage; discontinuous anecdotes compete with alarmist cable-news packaging—reflects rather than clarifies the issue’s complications. Clearly designed to wake up the whole red-blooded world, Primum Non Nocere plays like an underground video for radical med students.