What is the relationship between the contract curve and perfect substitutes in economic theory?

In economic theory, the contract curve represents the set of points where both parties in a trade can benefit. When dealing with perfect substitutes, where two goods can be exchanged at a constant rate, the contract curve is a straight line connecting the two goods. This means that any point on the contract curve is equally preferred by both parties, as they can trade one good for the other at a fixed ratio.