Karl Langer spent the 1800s doing some relatively gruesome experiments on cadavers. What he discovered is still of use to surgeons today.
Karl Langer spent most of the 1850s attacking people with spikes. In his defense, those people were dead. Langer was interested in the underlying structure of the skin. The skin gets its semi-elastic properties from collagen fibers embedded within it. Those fibers are not oriented the same way throughout the body.
Langer noticed that, when he pierced the skin of a corpse with a round instrument, the resulting hole was not round. It was pulled into an oval by the underlying tension in the skin. It occurred to him that surgeons who made incisions certain ways might be making cuts that cause the skin to pull itself apart. As convenient as that seems when making the incision, it had to hinder the healing process. The skin would have to knit itself up against the strength of its own pull.
To determine which way the skin pulled all over the body, Langer got bodies and systematically pierced the skin at regular intervals with an ice-pick-like instrument. He noted which way the skin pulled the little holes he had made. He then painstakingly diagrammed the direction of the skin pull for the entire body. You can see one of his early diagrams above.
Langer's work paid off, though. Although surgeons debate whether Langer Lines are really the best way to cut in all cases, his research has provided useful guides for certain surgeries - especially cosmetic procedures. Doctors can account for how the skin will respond to the cuts they make to minimize trauma and scarring. It also has told scientists a great deal about the underlying structure of the skin.
Still, just imagine how creepy it would look on an actual body. If a medical student had wandered in they would have thought that Jack the Ripper had taken up pointillism.