Disputatio medica, de cibo et potu

XIV.
If it moves according to nature, it is called a healthy and conserving cause, because it either conserves health or restores it when lost.

XV.
If, however, it moves contrary to nature, it is called an unhealthy, altering, or rather, a disease-causing cause, because it casts health out of a good state.

XVI.
The method of knowing whether this non-natural thing is sometimes healthy or sometimes unhealthy requires that two primary intentions or indications be held and observed.

XVII.
The first of these is taken from the quality and quantity of the non-natural thing itself, which is to be administered and exhibited.

XVIII.
The second is taken from the quantity and quality of the body itself, which is in need and necessarily requires food and drink.

XIX.
Just as other non-natural things are referred to the bodies to which they are applied, so also this one, of which we speak here, must be referred to the body to which it is applied.

XX.
It is referred either to different bodies at the same time, or to the same body at different times.