The exact wording is below. The priest says the "Amen."
P. Corpus Domini nostri Jesu Christi custodiat animam tuam in vitam aeternam.
R. Amen.
P. May the Body of our Lord Jesus Christ preserve your soul unto everlasting life.
R. Amen.
I find myself at an N.O. Mass whispering "Corpus Domini nostri Jesu Chrisi custodiat ANIMAM MEAM in vitam aeternam. Amen" as I approach communion in line. It is totally exhilirating...