Reply Obj. 2: The union of soul and body ceases at the cessation of breath, not because this is the means of union, but because of the removal of that disposition by which the body is disposed for such a union. Nevertheless the breath is a means of moving, as the first instrument of motion.
Reply Obj. 3: The soul is indeed very distant from the body, if we consider the condition of each separately: so that if each had a separate existence, many means of connection would have to intervene. But inasmuch as the soul is the form of the body, it has not an existence apart from the existence of the body, but by its own existence is united to the body immediately. This is the case with every form which, if considered as an act, is very distant from matter, which is a being only in potentiality. _______________________
EIGHTH ARTICLE [I, Q. 76, Art. 8]
Whether the Soul Is in Each Part of the Body?
Objection 1: It would seem that the whole soul is not in each part of the body; for the Philosopher says in De causa motus animalium (De mot. animal. x): "It is not necessary for the soul to be in each part of the body; it suffices that it be in some principle of the body causing the other parts to live, for each part has a natural movement of its own."
Obj. 2: Further, the soul is in the body of which it is the act. But it is the act of an organic body. Therefore it exists only in an organic body. But each part of the human body is not an organic body. Therefore the whole soul is not in each part.
Obj. 3: Further, the Philosopher says (De Anima ii, 1) that the relation of a part of the soul to a part of the body, such as the sight to the pupil of the eye, is the same as the relation of the soul to the whole body of an animal. If, therefore, the whole soul is in each part of the body, it follows that each part of the body is an animal.
Obj. 4: Further, all the powers of the soul are rooted in the essence of the soul. If, therefore, the whole soul be in each part of the body, it follows that all the powers of the soul are in each part of the body; thus the sight will be in the ear, and hearing in the eye, and this is absurd.
Obj. 5: Further, if the whole soul is in each part of the body, each part of the body is immediately dependent on the soul. Thus one part would not depend on another; nor would one part be nobler than another; which is clearly untrue. Therefore the soul is not in each part of the body.
On the contrary, Augustine says (De Trin. vi, 6), that "in each body the whole soul is in the whole body, and in each part is entire."