Worship and Authority
Eucharist Summary:

It is believed that through a ritual consecration, bread and wine are spiritually changed into the body and blood of Christ.  Baptized Christians then “eat and drink the body and blood” of Christ.  The sacrament’s ritual is based on the actions and words of Christ the day before his death, at the “Last Supper.”  During the late Middle Ages, the privilege of receiving the Eucharist was greatly desired but frequent reception was discouraged.  The elevation of the host during Mass, when the “sacring bell” was rung, the exposition of the consecrated bread in a monstrance often substituted for reception. In 1357 the Lay folk's catechism defined sacraments, naming the Eucharist the fourth:
The fourth is the sacrament of the altar
Christ's own body in the likeness of bread
As whole as when he took it from that blessed maiden,
Which every man or woman who is of age
Should receive every year:
That means, at Easter, according to the custom of Holy Church
When they are cleansed of sin through penance. . .
For he that receives it worthily takes it to his salvation
And whoever does unworthily, to his damnation. 
The Layfolk's Catechism, or the English and Latin Versions of Archbishop Thoresby's Instructions for the People. Ed. T. F. Simmons and H. E Nolloth (EETS 118) London, 1901, lines 316-22 and 326-7, p. 66.

See:
Duffy, Eamon. The Stripping of the Altars: Traditional Religion in England 1400-1580. New Haven: Yale University Press, 1992.
Rubin, Miri. Corpus Christi: The Eucharist in Late Medieval Culture. Cambridge: Cambridge University Press, 1991.