In Dar es Salaam, Tanzania — a city where HIV infects 40 percent of injecting drug users and tuberculosis infects even more — an unusual partnership has developed between two women. Fatuma Chande sells heroin to local addicts, and Rehema Mpili, a nurse, hands out clean needles in the drug den to make it a little safer. Both admit that harm is being done, but they also take pride in the fact that their arrangement is helping to make their neighborhood healthier by reducing the rates of HIV, tuberculosis and even drug addiction itself. In “The Street of Blood and Smoke,” PBS NewsHour’s Jason Kane takes readers into some of the most dangerous corners of Tanzania’s largest city to understand the stakes behind the highly controversial theory of “harm reduction.” Weaving together the opinions of public health officials — whose statistics demonstrate the effectiveness of needle exchange programs — as well as the the concerns of influential critics who worry that the practice will encourage drug use, and the immensely personal stories of a reluctant drug dealer and a recovering addict-turned-health worker, Kane illustrates how the wellbeing of strung-out addicts in a distant city can impact the health of the global population — and why the method to keeping them healthy might be as counter-intuitive as hand-delivering the tools they use to get high.