Raygat's test is based on:

Hydrostatic test/ Raygat's test: Principle: Specific gravity of lung before respiration is 1.04-1.05 and it becomes 0.94-0.95 after respiration. This makes the respired lung to float. Procedure: Dissect out the fetal lungs & Put into a trough of water and observe. Liver is used as control Inference: If they sink--unrespired lung. If they float--remove them from water, cut into small pieces and then squeeze or compress firmly between sponges, and again put into water. If they sink--unrespired lung. If they float--respired lung. Explanation: Floatation observed for second time is because of residual air that remains in the lungs which cannot be squeezed out by pressing, if the fetus has breathed after bih.