Limulus Amebocyte Lysate (LAL) is a substance derived from the blood of the horseshoe crab. It is primarily used in medical testing to detect bacterial contamination in pharmaceuticals and medical devices. The blood of horseshoe crabs contains amebocytes, which clump together in the presence of bacterial toxins, making LAL a reliable indicator of safety. The use of LAL is crucial in ensuring that products like vaccines and intravenous drugs are free from harmful bacteria. This testing method has become a standard in the pharmaceutical industry, helping to protect public health by preventing infections caused by contaminated medical products.