The control of intestinal infections has been a major aspect of the aggregation of human populations in large cities. By the mid-twentieth century, water and sanitation infrastructures in developed nations had controlled mortality from diarrheal diseases, but in the developing world many people still suffer and die from these diseases each year. Historically, intestinal infections have been the major cause of death in countries with contaminated water, inadequate sewage systems, and weak public health organizations. Even in developed nations, large cities became sustainable only after adequate preventive infrastructures were constructed. Cholera was the most dreaded of these diseases. It could kill within hours, reducing a previously healthy person to a skeletal appearance and causing death due to cardiovascular collapse. Cholera typically struck in community outbreaks and dreaded recurrent pandemics that have killed millions of people. Dr. Eugene Gangarosa's 50-plus-year career spanned the introduction of modern treatment, control, and prevention of intestinal infections in developing countries. By taking intestinal biopsies of patients with active cholera, he showed that the intestinal wall was intact, indicating that the disease was caused by a biochemical, and not an anatomical, disruption. Ultimately, this finding inspired other scientists to develop oral rehydration therapy (ORT) a simple and inexpensive technique to replace fluids and electrolytes lost through vomiting and diarrhea that could be administered at home by caretakers. As a result of rehydration therapy, both intravenous and oral, now even cholera can be effectively treated with little loss of life. The World Health Organization heralded oral rehydration therapy as "the medical advance of the twentieth century", estimating that it had saved over 50 million lives in the first 40 years since its development. Dr. Gangarosa also demonstrated the impact of frequent intestinal infections on physical growth via environmental enteropathy, a malabsorption syndrome that causes significant impairment in developing countries. This chronic component of repeated acute infections is a powerful motivation for prevention measures. One of his faculty, Aftim Acra, proved that direct sunlight could disinfect contaminated water. Dr. Gangarosa later played a role in the Centers for Disease Control and Prevention (CDC)'s Safe Water Program in the development of other technologies and strategies for enabling homemakers in developing countries to collect, disinfect, store, and use water with greatly reduced risk of disease transmission. Since intestinal infections are especially hazardous in infants and young children, ORT has been vitally important in reducing infant mortality and promoting developmental growth. This, in turn, has had a major impact in initiating the demographic transition in many parts of the developing world, in which parents reassured of the survival of their children have smaller families, retain more resources, and educate their children. In a world burdened with population increase and poverty, the control of intestinal infections has played a major role in solving some of humanity's most pressing problems. Dr. Gangarosa's own family history inspired his career commitment to safe water and sanitation, as four of his thirteen siblings died in infancy before his parents came to Americaultimately because of contamination and scarcity of water. He was the junior member of the team that first investigated cholera with modern scientific tools. Through the rest of his long and illustrious career, he has been involved in virtually every aspect of the prevention, control, and treatment of intestinal infections. Now he tells the story of the giants who inspired him in his fieldof which he himself is one.