xiv.); therefore, whatsoever thus disposes the body and thus renders it capable, is necessarily good or useful (IV.xxvi.

xxvii.); and is so in proportion to the extent to which it can render the body capable; contrariwise (II.xiv., IV.xxvi.

xxvii.), it is hurtful, if it renders the body in this respect less capable.
Q.E.D.
PROP.XXXIX.

Whatsoever brings about the preservation of the proportion of motion and rest, which the parts of the human body mutually possess, is good; contrariwise, whatsoever causes a change in such proportion is bad.
Proof .-- The human body needs many other bodies for its preservation (II.Post.

iv.).