The first detailed study of skin strength was carried out in the 1860s by Karl Langer, an Austrian anatomist working in Vienna.
mapped the natural lines of tension within skin by puncturing the skin on a cadaver with a circular tool and then measuring the shape of the resulting hole.
The tension within the skin makes these holes elliptical in a direction parallel to the tension.
Consequently, a simple measurement of the orientation of these ellipses allowed Langer
to map out lines of force in the skin over the entire body.
Today, these lines are known as Langer lines.