I am saying that anything has an essence and an accidental appearance. For example (as suggested by Calvin) a dove appeared to St. John as he baptized Christ but he identified that in essence it was the Holy Ghost (John 1:32).
Likewise, the eucharistic bread has every appearance (accident is the technical term) of bread. A laboratory will only discover bread. A zoologist at the scene in John 1:32 would only see a dove. The essence, or substance, of the bread is body, soul and divinity of Christ.
The scriptures say no such thing. It does not say that a Dove descended upon the Lord and that the Dove was an accidental appearance of the Holy Spirit. It says that the Holy Spirit appeared and "descended like a dove".
In order to get to your interpretation, the scriptures would have said that he saw a dove descend and that it was, in fact, the Holy Spirit. None of the gospels state anything like that. They are all in agreement that John saw the Holy Spirit "descend like a dove." Nowhere does it say he saw a dove descend. The scriptures merely state the manner in which the Spirit descended. The Holy Spirit did not become a dove, nor did it take on the substance of a dove nor was there the accidental appearance of a dove. The Holy Spirit appeared as The Holy Spirit and visibly descended "like a dove."
If Calvin stated that the Holy Spirit appeared in the physical form and substance of a dove, then Calvin was wrong. The scriptures say no such thing. It is an illogical stretch to turn that verse into some apologetic for the bodiliy presence of Christ in the eucharist.
Why must every speck of wine spilled or bread crumb dropped during the mass be consumed immediately by the priest?
What's the fear here?