Her first experimental work involved childhood diarrhea and confirmed previous studies on dysentery of bacilli with the disease. At the Rockefeller Institute of Medical Research, she collaborated on the first experimental polio work in the United States, worked on early investigation of pneumonia, and developed a method of preparing serum against antimeningitis with Harold Amoss. She was also a pioneer in early mumps research, suggesting, although not demonstrating, her viral nature. After 1921, Wollstein studied pediatric pathology in a children’s hospital, especially jaundice, congenital anomalies, tuberculosis, meningitis, and leukemia. He died on September 30, 1939 at the age of 70.