Groups like the New York Blood Center appealed to the public to donate blood on Sunday as dwindling supplies during the holiday season cause concerns.More than 250 people responded to the call by giving blood at Croton Harmon High School. Administrators who run the banks said the blood is badly needed around this time of year when supplies typically dwindle due to holiday emergencies. They said most blood blanks keep at least a three-day supply on hand, but anything short of that is dangerous.Medical professionals ask anyone eligible to donate blood to do so. The banks are particularly looking for type O donors, a blood type for which there's an acute shortage.