the third line of defense is the formation of specific antibodies to an antigen. This process requires exposure to various forally not capable of producing their own immunoglobulins until the beginning of the second month of life, but they receive considerble passive immunity in the form of immunoglobulin G(IgG) from the maternal circulartion and from human milk (seep.290). They are protected against most major childhood diseases,including diphtheria, measles, poliomyelitis, and rubella, for about 3 months, provided that the mother has developed antibodies to these illnesses.