The seventh chapter, “An Era of Optimism,” analyzes the new culture of sanitation practices that helped to define modernity. In the late nineteenth and early twentieth centuries, those living in the developed world became accustomed to wearing shoes, using toilet paper, bathing regularly with soap, and utilizing refrigeration systems to extend the life of foods. In the mid-twentieth century, populations in the Global North benefited from population-wide vaccination programs against poliomyelitis, the prevalence of which seemed to have increased as a result of the implementation of better sanitation systems. Based on the "hygiene hypothesis," many specialists believed that poliomyelitis was rare in regions without modern sanitation. This was not the case. Regrettably, polio vaccination did not begin in the developing world until the 1970s. Oral rehydration therapy, a major breakthrough in the treatment of diarrheal disease, saved millions of lives.