sentences:  In the Copenhagen epidemic of 1952, large numbers of patients were ventilated by hand ("bagged") by medical students and anyone else on hand, because of the large number of bulbar polio patients and the small number of ventilators available.In 1950 William Hammon at the University of Pittsburgh isolated serum, containing antibodies against poliovirus, from the blood of polio survivors.The serum, Hammon believed, would prevent the spread of polio and to reduce the severity of disease in polio patients.