At this point a drop of sodium hydroxide is added. If the trypsin has truly eaten through the gelatin, the sodium hydroxide is exposed to a layer of foil below, where it will begin eating a hole. With both the gelatin and the foil dissolved, a circuit is able to form between an iron salt at the cathode and a magnesium anode, lighting up the LED. If the LED lights up in less than an hour, the patient has acute pancreatitis.