Genre: 
Full text: 
Tantum ergo sacramentum veneremur cernui et antiquum documentum novo cedat ritui praestet fides supplementum sensuum defectui
Notes: 
See also: http://www.preces-latinae.org/thesaurus/Euch/Tantum.html where the last two verses are sometimes a separate hymn.
AH volume: 
50
AH item number: 
386