Question: There are three forms of baptism that are acceptable for salvation by the Roman Catholic Church. Infants are "baptized by affusion". What are the other two forms of baptism?
Answer:
Baptism of Water can be done in part by affusion (pouring water), immersion (submersion in water), or aspersion (sprinkling of water).
Baptism of Desire applies to those who die while wishing to be baptized and "Those who, through no fault of their own, do not know the Gospel of Christ or His Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do His will as they know it through the dictates of conscience."
Baptism of Blood refers to those martyrs who were killed for the faith before they had a chance to be baptized.
Read more:
http://happycatholic.blogspot.com/2006/04/back-to-basics-three-forms-of-baptism.html
http://catholicism.about.com/od/beliefsteachings/p/Sac_Baptism.htm
http://www.vatican.va/archive/ccc_css/archive/catechism/p2s2c1a1.htm