That is why, when the menstrual discharges occur because of a disturbance and bloody inflammation, the change in the eyes is not evident to us although it is present (for the nature of the discharges is the same as that of semen); and the air is moved by them, and has a certain effect on the air on the surface of the mirror which is continuous with it, ie it makes that air affected in the same way that it is itself; and the air on the mirror affects the surface of the mirror.