Bishop, however, exaggerates when he talks about the cult of the Blessed Sacrament as absent through the whole middle ages. The thirteenth century shows a dawning awareness of something more profound. A 1260 ordinarium from Zurich finds it necessary to explain that it is "contrary to reason ... altogether absurd" that "the Eucharist, which is the true living Body of Christ, should represent his dead Body". In the same century a conventual ordinal preserved in Dublin ordered the Sacrament to be "honourably reserved for the use of the sick", but less than a century later another hand feels it necessary to add "and for the devotion of the choir".
There is a red herring to be disposed of here. Dix, engaged in tweaking the tails of Anglican bishops who attempted to issue 'regulations' banning Corpus Chisti processions, loved to point out that the first records of Processions of the Blessed Sacrament were in Palm Sunday processions at Canterbury. Fair enough; the bishops of Dix's day were for the most part ignorant bigots. Indeed ... but let's not venture down that digression. But Dix is perpetrating, in my view, a genre confusion. On Palm Sunday, Christians in many parts of the Latin West desired to actualise ritually the Lord's Entry into the Holy City. They used, sometimes, a wooden statue of the Lord on a donkey; or the Book of the Gospels; or ... sometimes, the Sacrament. The genre is Drama and so the question is: We are doing a dramatic representation of a historical event, the Lord's Entry into Jerusalem: therefore how do we symbolise the Figure of Jesus? But the genre of the Corpus Christi Procession is not Drama but Adoration: we possess the true body of the living Christ: therefore how should we worship Him?
Once you stop thinking of the Sacrament Reserved as the real but dead Body of Christ which the Faithful need to receive when sick or dying, and begin to see it as the living Body of the living Christ, you will see it not as a supremely potent but dead relic but as the locus for a direct, lived, relationship between believer and Lord. We see this transition in the development of some of the very rare, early, processions of the Host before the end of the thirteenth century. The host was processed together with the other most potent relics of the Church concerned. But such practices soon became much less common, and eventually disappeared.
And this revolution led to a change in the vessels used for Reservation. No longer were they made of ivory, but of precious metals. No longer were they designed to represent the Sepulchre at Jerusalem. Above all, no longer was the Sacrament to be reserved in the same vessel as the Holy Oils*.
*In the first millennium - remarkably, to our minds - the vessel blessed to be a container for the Sacrament was often called the Chrismale!