Immunizing Sera as Vaccines -
An immunizing serum (plural 'sera') is the actual blood serum of a person or animal and contains an immunizing material or antibody. It is generally obtained by injecting a toxoid into an animal (usually a horse), permitting establishment of active immunity in the animal, and then withdrawing some of its blood.

The corpuscles are removed from serum, which is then standardized as to the strength of antibodies and stored in sterile tubes or bottles.

Immunizing sera are used mostly for cure rather than prevention. They may be given for prevention after exposure has taken place, but their immunizing effects are too short lived to give any benefit if administered much in advance of the disease.

As a curative agent, the action of immunizing serum is very rapid. Immunizing serum has been used in the cure of diphtheria and tetanus.