Flags flew at half-mast across the University yesterday as school continued uninterrupted in the aftermath of Tuesday’s tragedy.

College classes met as scheduled yesterday, and classes resumed at the medical school, the law school, the business school and the Kennedy School of Government after cancellations on Tuesday.

“It just seemed weird, it was too soon,” said Trevor D. Dryer ’02 of the efforts to return to normalcy. “It was like there shouldn’t be a day or two [of remembrance].”

But signs of Tuesday’s attacks were still visible across campus, from the continued, stepped-up presence of uniformed officers to posted signs offering counseling services. Overhead, military planes cruised the airways.

At the checker’s desk in Adams House, a glass pitcher for cash donations and a sign-up sheet for the University Health Services (UHS) blood drive were silent reminders of Tuesday. Lowell House continued to offer residents free long-distance calls to New York and Washington D.C. from the senior tutor’s office. Many professors cut classes short or prefaced their lecture with a moment of silence.

“In every single one of my classes, it was discussed,” said Dana A. Gavrieli ’02. “The professors were great in terms of addressing what happened.”

More than a thousand students signed up to participate in UHS’s blood drive, which kicked off yesterday.

UHS Director David S. Rosenthal ’59 said the drive will likely continue through Friday, depending on whether hospitals continue to accept donations. Buses hired by UHS have also been bringing volunteers to Children’s Hospital and Brigham and Women’s Hospital, where the wait to donate blood is still significant.