Thomas Aquinas

“ By the power of the sacrament there is contained under it, as to the species of the bread, not only the flesh, but the entire body of Christ, that is, the bones the nerves, and the like. And this is apparent from the form of this sacrament, wherein it is not said: "This is My flesh," but "This is My body." Accordingly, when our Lord said (Jn. 6:56) : "My flesh is meat indeed," there the word flesh is put for the entire body, because according to human custom it seems to be more adapted for eating, as men commonly are fed on the flesh of animals, but not on the bones or the like. ”

“ But the blood is one of the parts of the human body, as Aristotle proves (De Anima Histor. i) . If, then, Christ's blood be contained under the species of bread, just as the other parts of the body are contained there, the blood ought not to be consecrated apart, just as no other part of the body is consecrated separately.
Objection 3: Further, what is once "in being" cannot be again "in becoming." But Christ's body has already begun to be in this sacrament by the consecration of the bread. Therefore, it cannot begin again to be there by the consecration of the wine ”

“ On the contrary, Augustine says in a sermon (Gregory, Sacramentarium) : "Each receives Christ the Lord, Who is entire under every morsel, nor is He less in each portion, but bestows Himself entire under each." ”

“ Number follows division, and therefore so long as quantity remains actually undivided, neither is the substance of any thing several times under its proper dimensions, nor is Christ's body several times under the dimensions of the bread ”

“ And not even the angelic intellect of its own natural power is capable of beholding it; consequently the devils cannot by their intellect perceive Christ in this sacrament, except through faith, to which they do not pay willing assent; yet they are convinced of it from the evidence of signs, according to James 2:19: "The devils believe, and tremble." ”