Book 4
22
Asclepiades supposeth the lungs to be in the manner of a tunnel, and maketh the cause of breathing to be the fineness of the inward parts of the breast; for thither the outward air which is more gross hastens, but is forced backward, the breast not being capable either to receive or want it. But there being always some of the more tenuous parts of the air left, so that all of it is not exploded, to that which there remains the more ponderous external air with equal violence is forced; and this he compares to cupping-glasses. All spontaneous breathings are formed by the contracting of the smaller pores of the lungs, and to the closing up of the pipes in the neck; for these are at our command.
