Of these four processes two are dilatations, one when the lungs attract the air, another when the breast dischargeth itself of it upon the lungs; two are contractions, one when the breast draws into itself the air, the second when it expels this which was insinuated into it.

The breast admits only of two motions--of dilatation, when it draws from the lungs the breath, and of contraction, when it returns what it did receive..