The first aliyah gives some commandments pertaining to the special behavior of Kohanim in their everyday lives. Included here is that a Kohen shouldn't participate in the handling of any deceased people except for certain close relatives. Also, a Kohen shouldn't even go under the same roof as a dead person, and Rashi here defines a dead body as contact with merely a riviis (about 3.5 ounces) of blood. (This commandment has implications for Kohanim today entering a hospital for a non-emergency, and attending funerals.) This aliyah also specifies whom a Kohen may marry.