A blood transfusion is the transference of some of a person’s blood directly into the circulatory system of another. This is done to replace lost blood or to treat blood diseases, and in many cases is a life-saving procedure.
When Dracula was written, blood transfusions were still a relatively new procedure, and were often unsuccessful. This was because scientists had not yet discovered blood groups, as is evident from the fact that Lucy is given the blood of four different men without testing! It is essential to ensure the donor and receiver’s blood types are compatible when transfusing, as otherwise the blood can clump or agglutinate, with fatal consequences. It wasn’t until 1901 that Karl Landsteiner discovered blood groups (A, B, AB, O), for which he was awarded the Nobel Prize.