Nancy Linn attended a memorial service for her husband, Arnold, last week. For months, medical and nursing students at Georgetown University had explored his body and those of 64 other donors in the anatomy lab. They learned about disease and about complexities of the human body. Now classes were over and the school was holding its yearly anatomical donor Mass, to say thank you. In a classroom auditorium, about 135 family members watched as a procession of 160 white-coated students walked down the aisles on either side of them. Each placed a glass-held candle on stage with a gentle clink, creating a seemingly endless chain of light.