With ya so far, Fr. David

Carry on!
That’s the one reply I was not anticipating!
Most of the time, the substance of something and the accidents of something are “the same.” A bar or iron has both the accidents of iron and the substance of iron. A loaf of bread has both the accidents of bread and the substance of bread. This is true for everything in the natural world (although the ancients did not necessarily always see it that way).
Substance can be changed.
A bar of iron (accidents and substance) can be changed into a pound of nails. Each nail would have the accidents and substance of nails.
A tree has the accidents and substance of a tree; but one can take parts of that tree and make them into lumber. Accidents and substance of lumber.
Take nails and lumber, put them together. One now has a table. Accidents and substance of a table.
Accidents and substance are something that can be changed by everyday actions. However, they always “go together” meaning that if the accidents are changed, the substance likewise changes. The table does not have the substance of a tree–instead it has the substance of a table (table-ness) because it now has the accidents of a table (flat top, legs, etc).
The point here is NOT to think like a modern-day thinker and say “wood is wood; therefore a table has the same substance as a tree.” No. Substance doesn’t mean “what it’s made out of” but “what it IS.” It has tree-ness or it has lumber-ness or it has table-ness.
We can change the accidents of something and this causes the substance to change (tree-ness into table-ness); but keep in mind that one cannot change without the other changing.
The only way that something can have the accidents of A but have the substance of B is if a miracle occurs.
That takes us back to the original question.
When we drink wine, we get drunk. This happens not because “we drink wine” because the substance-alone of wine cannot actually do or cause anything. The substance of wine is nothing more than it’s “wine-ness.”
It’s the accidents of wine, in this case it’s chemical properties and the fact that it contains C2H6O (yes, I had to look it up) and what effect that has on the human body, which make us inebriated.
Substance by itself cannot do anything. Substance is more of a concept than it is a physical reality.
Before the consecration, the accidents of the wine are “attached” to the substance of the wine. Not attached in the sense of physically connected (since substance is an idea but accidents are physical properties), but philosophically connected.
By the consecration, the substance of the wine no longer exists, but has been replaced by the substance of the Blood of Christ–hence transubstantiation. However, the accidents of wine remain. This is the miracle. Normally, the accidents of a thing are attached to the substance. In the consecrated Eucharist, the accidents of wine remain, but they remain “unattached” to the substance of the Blood of Christ–meaning that we have the substance of A but the accidents of B (remember that normally, if we have the substance of A we necessarily have the accidents of A). This difference between the accidents and the substance can only happen by a miracle.
Conclusion: Since the accidents of bread and wine remain in the Eucharist, all of the results of those accidents (like a reaction to the gluten in the wheat or a reaction to the alcohol) still happen; but those reactions are caused by the accidents, not caused by the substance.
Again, I’ll stop here and await a response.