no,it isn't . there are some small but important differences.in the past, people sometimes died after they received blood from another person (a donor). nobody understood this until 1901 when the Austrian scientist , Karl Landsteniner,discovered that ther are four main types of blood . some types of blood can mix together in the body without problems, but some combinations become solid and the blood can't move around the body . Landsteiner called the blood types